The only things that register on the party scale are two things. One the socializing. They don't care about the deco, what the food is or the bar. You could stand in a padlock with no lights so long as there was some food (a fridge will do) and a stereo and just talk and smustle the whole time and they would get a good score.
Two is to do the set items that the party requires. So for a wedding that is the wedding and cutting the cake and for a birthday that is blowing out the candles. House warming parties are harder as they don't have anything set and neither do sport parties. Watching sports does nothing for the score.

My parties always turn out well; I don't know how

If I'm not mistaken, the key to good parties is lots of double-plus interactions (things like red hands, hug, gossip, dirty joke, etc.).

Just invite a lot of people who like each other and they'll take it from there.

Eugh I just hosted a "New year bash" or whatever that was a snoozer. Don't even know how. I invited a lot of people who were all friends, all became best friends with each other, music was playing, about 10 people were smustling at any given time, everyone was having a good time.

Usually I do this and I get a "great party" or a "roof raiser". I have no idea what I do at some parties to get them to be better than others. Hmm.