When creating a Sim, there are several basic personality traits that you can customize based on what you want your Sim to be like. You can either choose an astrological sign for your Sim that will determine its traits or you can just choose them yourself.
Neat[edit]
Neat dictates how likely your Sim is to clean up after itself. While you can hire a maid to clean up after your Sim, you'll end up having to pay her more if she has more to clean up. It is helpful to have a neat Sim in Get A Life, especially when you're living with Mimi/Dudley.
Playful[edit]
Playful is a measure of what your Sim likes to do for fun. A more playful Sim would rather play a game or watch TV for entertainment while a more serious Sim would rather read a book or the newspaper. Overall, this isn't too important.
Outgoing[edit]
Outgoing sims require more frequent socialization than shy sims.