Most of the guys I have been interested in were my friends first. Other than that, I've really just met guys at bars or parties. That usually involves some flirty eye contact, then going over and introducing myself.
I agree with quinceykay that it's best to avoid the pretending to bump into him, finding out who his friends are etc. Not only can that be childish, it could come across as creepy. I know if a guy did those things to me, it would be a turn off.