When I'm in CAS, I tend to make Sims with uniquely-colored blue or green eyes and average builds. For female Sims, I'm a big fan of dark red hair and heart-shaped faces. For the males, I like to use a little facial hair (if it looks okay) and shorter hairstyles. Sims I create tend to always have the Friendly or Charismatic trait. Typically, all items in my Sims' wardrobes are customized in Create-a-Style. If I'm creating a family, there will always be at least one Sim who's self-employed. I love that feature from the Ambitions EP.
Regarding the architectural aspect of The Sims 3, I'm not much of a builder, but I love redecorating homes that are already built. I spend entirely too much time in Create-a-Style customizing everything. When I don't feel like actually playing, one of my favorite things to do is redecorate townie homes.
I almost always play in Sunset Valley or Hidden Springs, but I'm trying to get better about branching out and playing in other towns. I tend to gravitate towards the ones I know best, though. I love playing townies. I find their backstories interesting, and it's always fun to give them makeovers and play with genetics.
When I'm not playing a challenge file, I typically disable aging for a while because I feel the town ages too fast. I used to always use
motherlode and place my Sims in an expensive, luxurious house from the get-go, but now I enjoy the challenge of working towards riches. Some of my other habits are always completing my Sims' Lifetime Wishes, picking lots with the Beautiful Vista moodlet (if I'm able to), pausing the game too much to catch my Sims' expressions--pausing too much in general--and not playing past the second generation. Lol. Admittedly, I'm extremely fickle in The Sims 3 and will often get bored with a file after the second generation and start a new game. I'm trying to get better about my last habit, but I always want to try something new in the game.