SF is a small city - a bit like DC - not at all like NYC, except that SF is a bit expensive right now - everywhere - like NYC. Residents think it is a very sophisticated place (maybe it is compared to DC), but in reality, it is a pretty but very provincial place - but with a lot of gay men. It is known for the variety of cuisines of restaurants.
Neighborhoods: - anywhere except the outer areas is good. The Castro, which used to be exclusively gay, is now about one half gay - still a great place to live. A lot of young people tend to live in the South-of-Market area - or towards Mission Bay (newly developed housing) or near Market Street (e.g., Hayes Valley), or in the Mission. The Marina is the ultimate young straight neighborhood. You should find some temporary housing while you explore and find out where you really want to live. Some brave souls are doing the "urban pioneer" thing, and moving into the Bayview (at least on the edges) - most of the street shootings occur in the middle of the night there, If you have a car, you will find that parking is very difficult in some neighborhoods. Some people do without a car, rent one on weekends, or park it in an outlying neighborhood. On-street parking is easily found in the Castro and Noe Valley. If you are working at one of the high-tech firms down the peninsula, they provide free buses into the city.
In San Francisco, locals refer to it as "The City" - never "Frisco." Four-to-six lane divided highways are always called "freeways," and, for example "101" or "280," - never "the 280," or "the 101."