As a straight guy who has gay friends, I'm often jealous of guys being able to go to a gay bar and pick up someone. As said above, gay bars tend to be about one thing, hooking up and getting some. 'Straight' bars aren't quite the same. If I were you I'd head to a gay bar, sit at the bar (with friends or not) and check out the talent, chat to anyone at the bar and be friendly, chances are you'll either get a chance to try on some moves or you'll have some tried on you.
As with any 'pick up' situation, you aren't going to succeed all the time so don't be worried if it doesn't go perfectly the first time - no one can be that lucky! Just enjoy yourself and see what happens.