I don't really have a preferred way to start a save. I mix it up to whatever interests me at the time, and whether I'm doing a challenge or not.
Most of the time I start with a single sim created in CAS and have them meet a love interest (often at university), but occasionally I start with a steady couple. It all depends on what I want to do with that game.
Usually I start my sims in a starter house, but I've done the rags to riches thing (staring my sim on an empty lot with no money), and I've had a sim couple start on an empty lot and immediately enroll in university to make money and later moving into a nice home once they've graduated.
I'll customize worlds before I use them, but I don't make over an entire neighborhood.