Note: If you made your Sim using Body Shop, you can package your Sim that way and share them wherever you want. This is how you can package your Sim that you made in Create-A-Sim (CAS) or any other Sim already in-game:

You will need SimPE and you can download it here.

After it has been installed, launch SimPE.

Go to Tools (top menu). Choose Neighbourhood in the menu.

Click Neighborhood Browser.

Choose your neighborhood.

Then go back up to Tools/Neighbourhood.

Choose Sim Surgery.

Find your sim. On the right side choose use under the top square box.

Once you do that the word Export above that same box where you sim picture should now be will be in blue.

Click Export.

And you're done!! EASY!! Your sim will now be in your Saved Sims folder and show up in BS and CAS. :D

(Originally written by SilkStockings and found here.)