We can give you a couple of pointers, but everyone is not going to have the same interests or the same favorites. Even if you want to steer clear of the big tourist attractions, you can't miss Alcatraz. It's fantastically preserved and the guided tours are excellent.
Boat ride across is pretty cool too, so check it out.
If you get worn out by the people watching, stop for a snack at any of the little eateries which line the blocks. Stroll the Golden Gate Bridge Bundle up, but do it. It's a great way to view the Bay Area. The Castro is a term used to describe the area of San Francisco formerly known as Eureka Valley. Much of the gay and lesbian community of San Francisco lives and works in the Castro.