I gave a "love" to the original post because it has been very interesting reading all of the varying replies. So many different playstyles!

I almost have TOO much to say on the topic, having played Sims 2 since it came out, but I will talk only about my current project, my Alien Transformation of Sedona (link to Simblr, with loads of pix, in signature, for the curious)

As surely everyone knows, I didn't make the original version of the town..that was the work of The Hood Building Group here on MTS. I didn't make the original four men you start with either, nor did I build the starting houses or the one community lot.

What I did do was transform the landscape with terrain replacements, water recolors etc, added in a lot of my own buildings, some downloaded ones by others, a load of neighborhood deco and a few additional sims.

I had just come off of playing Sims 3 for the past few years and liked the colorful custom alien worlds I'd been playing. I liked the views from my sims houses.
I wanted to go back to the gameplay of Sims 2: more stable game overall and Sims 2 Sims seem more emotionally "real" and passionate somehow, were the two main reasons. But I liked my exotic alien worlds too..what to do? Sims 4 did not look to be the ideal "love child" of both games i had been hoping for. So, how to achieve a Sims 2 game that approximated some of the elements I liked in Sims 3?

I had been testing out a few ideas for achieving an exotic alien world in a throwaway neighborhood when I read about the Sedona Neighborhood and backstory. It amused and inspired me. I got an idea to use this as the starting off point for developing a divided alien colony, with those original men literally in the middle of two very different "cultures"

When I play a neighborhood, I become quite invested in it and can only focus on that neighborhood. I have never quit a neighborhood willingly..it was always some disaster that ended me playing it. (corruption first time, second time sudden computer death AND the simultaneous death of the ONE back-up device I had at the time. I now back up regularly onto TWO different external hard drives and a mess of flash drives..I will never lose a 'hood like that again!)

Sedona is being developed very much with long term gameplay in mind. Avoiding corruption, not overbuilding in the beginning because I know my later generations will need room to expand into and, an additional set of factors:

Each building MUST enhance the overall alien exotic "mood" of the town and HAS TO look good both in neighborhood view and from other lots.
Each building has to be situated so that the view from it is maximized.
I am allowing room for later generations to own businesses and venues, so keeping those at a minimum at the moment, but I'm not following the strict rules of some of the challenges where you lift restrictions and such.
I am trying to get that sense of a large, connected, organically growing world

As far as families, the descendants of the four men are the focus. All other sims I've introduced to the world are secondary characters who are played only as much as needed to develop them in relation to the main families.

My goal is to see which alien faction the descendants fall in with..who they befriend as they grow up will determine where they will "feel comfortable" and settle in adulthood. The town, and eventually, subhoods, will develop according to which cultures seem to be having the most influence.
It is possible of course that the children of secondary families in either of my two parts of town will develop in unforseen directions and further complicate things..I will let the story go in whatever direction it takes based on scenarios that arise.

The surprise element keeps it fun for me. I have a strong preference for playing born-in-game sims. I like dealing with the surprise of their looks. It can be a fun challenge to style them. I get more attached to them also because I have seen them develop. They have history that arose in my game, that I witnessed.

I like to have a self-sustaining town. This means Sims grow their own produce or buy it in local stores that are run by farmers. There are no NPCs, meaning that when I need a repairman I summon a playable who is the repairman of the town, make him selectable and repair stuff. The same goes for maid etc.
Then there are no Maxis careers, everyone in town has his own role. I have lots like hospitals, fire station, police station, where playable Sims work as doctors, police men etc. Then office buildings, science station, etc.

Sims have their own businesses and all the playables have jobs through them. There are no townies in my hood. When I visit a community lot, I want to see other playables serving the sims who visit.

I also wanted to do a Bacc-challenge, but I don't have the patience for it. I love laying out the neighbourhoods completely with all of the important lots.

Currently I'm playing in my own Uberhood that I created using these files:
http://meetme2theriver.livejournal.com/63030.html

My main hood is Downtown, which is a bustling city with various rich and poor homes and businesses. Then I have three subhoods, one created from scratch. I attached the original Maxis neighbourhoods as business districts so that I have all the premade Maxis Sims from Pleasantview, Veronaville etc. To avoid hood corruption I moved all the graves to Downtown so that I could delete the subhoods I don't use.

Now I'm in the process of starting the self-sustaining hood I described. My mayor is Cassandra Goth.

Here are links which describe such a game principle better than I did:

This is a more recent one:
https://pennysims.dreamwidth.org/1341.html

And the original concept is from Jade Elliott (Isle of Thyme). You can find a tutorial here:
http://www.mediafire.com/view/jj9or...d_Tutuorial.rtf

I also love FSBS (for Sims by Sims) Communities. The one I like most is Simmington Hills (not maintained anymore):
http://simmingtonhills.blogspot.co.at/

To go a little more in-depth than I first did..I do write up info in notepad, saved in documents, of each Sim. Their aspiration(s), signs, personality, LTW, etc. and any other factors I feel fit that Sim. Like Olive Specter is evil and only cares about her Son and his father. Circe Beaker is evil and cares about no one but what she wants, Loki does truly love Circe but she doesn't return the feelings.

I do need to make a list of Sims in all age groups and if they are with someone or not. I pair up playables with each other first, but if none is available or fits (I determine their sexuality as fits their character without bothering to think of what playables there are) I have no issue with adding in townies.

I find the Maxis storyline really helps get me going in those towns, or Strangetown currently. My Royal Kingdom is from the Royal Kingdom challenge so follows the rules of that challenge and I rolled for a lot of things, like aspirations, to make it easier on myself rather than trying to figure them all out myself and still maintain diversity. I then figured out what community lots I needed to start with, made them and...that's it.

For my Sci-fi hood I haven't started playing in it yet but i've made all the families and community lots. I just went with what I felt like worked for whatever skintone I was working with. Where they robots? Demons? Pixies? I have very minimal storyline, just enough to start with and then basically fly by the seat of my pants. I have the founding family, the richest. Some middle-class, some poor. Some races don't get along with others (but for the most part they don't care). I have an idea for each family of how they got to that planet and why they came to it, what they came with thus how much money they have, and what their personalities are like individually. And that is my starting point. I made needed community lots and some of the families own a business.

I guess i'm mostly a pantser?

I shamelessly stole some ideas from these posts, like from Justpetro, I stole the idea to make 12 sims in college (so i could make them with individual sir names), one for each zodiac. I made 6 women and 6 men, a man and woman for each aspiration, and 3 of each skintone. Face templates were randomised too, so I couldn't pick only "pretty" faces, or decide what faces would "blend" well.
I played them and let them decide who they wanted to date using "scope room" and picking who ever was most compatible.

Now they've left college and went home to a custom neighbourhood map that I made, [images attacked] (I call it "Stacks" because it looks like 4 long boxes stacked on top of each other. There are only 3 different sized lots, the biggest, 5x5, the middle, 3x4, and the smallest 2x3). I planned it out on MSpaint, 44 residential and 24 community lots (possible future expansion in a downtown and shopping district).

I built some community lots and right now everyone is "equal" but I plan to slowly add a class system.
The next generation will be the only generation I'll be adding extra CAS sims, but after that they'll have to breed within the hood.

I've decided for the hood to be self sustaining, and right now I have a "Llama Monster" sim that lives in a shack at the very edge of the map that will act as an NPC but he owns all the community lots and all the sims are employed in his businesses rather than maxis jobs. When my sims have enough money to buy a lot, they'll either buy a new (empty) one, or if i want them to take over an existing business, I'll have the Llama Monster sell the lot to the community and have the sim buy it like normal. I'm also thinking of making Llama Monster some kind of bad omen, and if you lose a fight with him (he's a mean sim so loves fighing anyway) you'll be cursed to die or something.
[attached a picture of Llama Monster, for fun. the blurred on is in black and white because my hood is set in an idealised version of 50's/60's America (but it's not solid, like I'll let them have cellphones and just say it's because of alien tech)]

This hood is kind of like a test hood for now. I'm going to slowly add in rules as I go along and see what sticks, and eventually I'll re-start with a batch of less randomised sims and play with my new tried and tested rule set :P

I'm really the opposite. I'm still playing the Veronaville I started playing the first time I started up the game. That will be three years at the end of this month. The other 'hood I play regularly is a custom island 'hood called New Desconia. I created it in January 2014 when I thought Veronaville was broken. It's a very escapist 'hood populated entirely by hedonistic young Romance Sims. So Veronaville is my "serious" game. New Desconia was the last proper 'hood I started. Since then I have only started a building 'hood (with no Sims at all) in my main game, and recently a base game test 'hood and a building 'hood in AGS.

So I very, very rarely start a new 'hood. I quickly become emotionally attached to my Sims, and I would feel I was letting them down if I didn't go on playing them.

I do plan, but the planning I did before starting Veronaville, seeing I had yet to start the game, was based on what I had read in the little printed manual that comes with the game. So I often had to change my plan as I discovered how the game was really played. My planning was all in my head and very vague. I planned Andrew as a gay teen, and always intended to make a boyfriend, for him, but I only named him on the spur of the moment, and his mum Gloria was an afterthought when I discovered the game wouldn't let me save Andrew without an adult relation. A very happy afterthought it turned out, because it rapidly became clear that Andrew and his mum thought the world of each other. And I quickly had to change my plan to give Gloria a boyfriend too. My plan was that they would marry and give Andrew a mum and dad, but I reckoned without Romance Sims fear of commitment. They are in effect faithful to each other, but they still haven't even got engaged. My original plan was to only play Veronaville till I got the hang of the game, but, as I said, I soon became very fond of my first Sims. I spend a lot of time planning in my head what my Sims are going to do next, but my plans are often reactive or have to be changed to accommodate my Sims' wishes.

My neighbourhoods start small, and Sims, lots and even sub-hoods get added over time. To begin with I only played my own Sims in Veronaville and pretty well ignored the pre-mades. Actually I treated them the same as townies -- my Sims might talk to them if they met at a community lot or walked by, but it took a few months before I started to play their lots. Initially I was playing 8 Sims in 3 families: the Jones's -- Andrew and Gloria at 19 Chorus Court, Garry Mackay, Gloria's boyfriend in a Ranch Retreat house across the canal on the Italian side, and the Moltke's, a German family of 5 living at 100 Via Veronaville -- Martin and Manuela are married with 3 children: Julian (teen - Andrew's boyfriend), Brigitte (child) and Hans (then a toddler but now a child too). After a couple of months I added a Downtown and about a month after that I worked out how to make Sims live Downtown. A gay teen in my first Downtown family seduced Puck Summerdream, and as consequence I began to play the pre-mades. Over a long period of time I moved the Family Bin Capps and Montys in, Goneril and Albany's big family being the last. I kept adding CAS Sims too, and, with various townies and Downtownies becoming playable, the playable population steadily grew. The last big increase to the population was when I added Bluewater Village about a year ago. There are now 29 playable households in total played in very loose rotations. Not all the Bluewater pre-mades have been played yet.

I wanted a swimming pool for my Sims from the beginning, so just after I started to play I built a big open-air swimming pool on the Italian side of Veronaville, just across the road from the Monty Ranch. When I first built it, it was little more than a huge swimming pool in a field; even the toilets weren't finished (because I was just learning how to build) and poor Andrew (a Virgo) got caught short when he went there to lose weight. In addition I had the 4 Maxis Veronaville community lots as the only places my Sims could visit. Adding Downtown of course greatly increased the range of possible destinations, but I also added a lot of community lots to Veronaville itself, mainly on the Italian side, the first ones being a row of Moos Mews lots. There are also a couple of fashion outlets, a large (by my standards) nightclub and restaurant, a church, and most recently a little privately owned grocery shop and a park. Today, with Bluewater Village added, and extra venues added to Downtown, my Veronaville Sims have a huge choice of possible destinations for their outings. There are quite a few of them that I have yet to visit. All of these things were planned to the extent that I thought about them before building them, but of course none (except the swimming pool) were planned, or even thought of, before I started playing.

New Desconia started with me downloading sedgez's Tiny Isle terrain. It was always intended to be quite small, and I started with 4 houses, a shop (Mootilda's convenience store), a park, two playable Sims and five townies. This quickly proved to be too small -- everybody turned up for every visit to the park -- and I quickly added 3 more CAS townies. It has since expanded to 25 playables and 28 townies, all created in CAS. To the original two community lots have been added two nightclubs (one of them owned by two ex-townies), a restaurant, and a pub. There is also a school (which technically is a residential lot). The population is now close to the maximum the island can accommodate if it's to retain any of its original rural appearance. Unless of course the founders find and colonise a second island as a sub-hood.

So in summary I'd say I do quite a bit of informal planning in my head, but very little of this is before starting the 'hood. I don't do any formal planning in advance at all - neither on paper nor in other computer programs. I have one small spreadsheet and a couple of Word documents to help me keep track of my Sims, but mostly just so I can check things when posting here without having to start the game and open the 'hood/lot concerned. Continued interest, at least in Veronaville, is maintained by me having a wide variety of different kinds of household living across the neighbourhood, and by me really caring about my Sims and wanting to see them.

Oh, what a fun thread. I ought to have guessed I'm not the only one who makes my sims deal with real world problems like racism.

For a long time I played legacy-style focusing on one family, but lately I have gotten into the Build-A-City-Challenge and am really fascinated by my emerging neighborhood. There's one side of town where all the sims of color live because if they try to move into the white area the white sims get upset. One black sim, Jeramiah, couldn't get a loan for his business. He was an inventive guy though and his wife was very good at robotics, so he had her create a servo for him which he named Botbot. The servo was able to take out the loan and buy the business, and then transferred the deed to Jeramiah's name.

I have a spreadsheet to keep track of my BACC details, but there are a few aspects of it I find too easy in comparison with the rest, and some aspects (like collecting taxes) are too fiddly and annoying to be fun. So I'm thinking about doing my own attempt at a new version of BACC rules that is point-based rather than dollar based. For certain events (sims growing to adult, sims getting jobs, businesses getting to rank 5 or 10) the player earns Tax Points, which can then be spent on building community-owned businesses or lots, or opening universities, business districts, and downtowns. It would also involve a re-work of the rules for career eligibility. But I want to play further along in my own BACC to get a better idea of what I want to keep and what I want to change.

I'd love a simplified, points-based BACC! If you do re-work the rules, please do post it here on the MTS boards in the challenge section.