If it's a sim for a brand new game I have very little in mind when I start. Sometimes I will know what career they'll be in, or maybe they'll be part of a sub-culture. Most of the time I just start trying on outfits and applying makeup and let the character emerge, making changes as I go.
Right now I'm only making new sims to fill specific roles in one of my two rotational saves. I still don't have a vision of their final look or personality, but half of them will have a career path and lifestyle pretty well set in my head when I start. I usually give them two outfits in every category except formal and party. My sims just don't find themselves in those situations very often. Formal almost never, and party on rare occasions. It's not that they don't go out, they go out a lot. The night's out usually aren't prearranged events, just someone calls up the group and says 'let's hang out at X', so party wear doesn't figure in. I keep meaning to make it a thing and then I just roll with whatever they show up in.
I don't give them likes or dislikes, with the exception of disliking mischief. I don't give that to everybody, but I do give it to most of them. It's my way of trying to rein in the use of mischief. Like a few things it's so completely overdone to the point of being irritating instead of funny.
