I have a few different standard ways I play.
1) START WITH SINGLE SIM. Create a teen or young adult female and start building their friends through townies and premades, find a partner, advance in career, start a family. I'm too controlling to just play that sim, though, even though that's my initial intention, so I end up playing some of the other sims in her circle so that their lives can intersect with hers in a more realistic way. For example, one of her friends will throw a party and invite her, so then I have to go set up the party. Or I'll get two of the people in her friend group together romantically. Stuff like that. I end up playing multiple households, but she's still the main focus.
2) CHANGE AGES TO MATCH MY SIM. This was one of my favorite ways to play. I wanted to play a young adult female who moves from the small town of Willow Creek to the big city of San Myshuno, but it bugged me that my sims start with no friends and no parents to attend their wedding. So I gave her a family and started playing her one age group lower from what I wanted in my main storyline. I made her a teen in Willow Creek. Then I aged all the kids in Willow Creek to teen so that she'd have a peer group. Once she aged up, some of her friends also moved to San Myshuno and some stayed in the same neighborhood, like they would in real life, and she would come back to Willow Creek sometimes for visits with family and friends, or her high school friends would occasionally come visit her. It was nice to start the "young woman moves to the big city" storyline with my sim having a backstory and social relationships already in place.
3) WHOLE WORLD. Create a whole world of my own sims in a different era (what I'm doing now--1800s).
4) NON-STANDARD COMMUNITY LOTS. This goes with all other styles of playing, but I like to create different lots, often generic, for my sims to interact in. Some lots I've created are corporate offices, schools, after-school centers, a place for Alcoholics Anonymous meetings, an art store, a multi-store shopping center on a single lot, a masonic lodge, a church, and the one I'm currently working on--a bank.
Oh and I always cheat to provide them with housing I think is appropriate to their personality and financial status. Sometimes making a home look poor actually takes a lot of money, so I rarely try to build up money for housing or decor.