Don't go up to a girl and say "hey, you're cute... wanna have sex?", get to know her first. Seek out your female friends, but don't be upfront. Casually start the discussion about relationships and sex, and get an idea of how she feels about it. If she says she wouldn't mind hooking up with a guy, then you can take it a small step forward. But don't go up to a friend and say you want to have sex with her, that'll scare her off. Plus, chances are, your female friends know you just got out of a relationship and don't want to be a rebound. Even if it's just for sex.