I've had the same sort of problems... and here's what I've done (Let's just say I'm a recovering AFC): TALK TO PEOPLE, ANYONE, EVERYONE!
Jjust get into the habit of speaking with anyone anywhere anytime. and especially speak with a lot of ugly girls, people you have no intention of dating, hooking up with, or maybe even being friends with. Just get into the habit of opening up and you'll start to naturally get the swing of things... and you won't be nervous or anything because it's almost like you're doing them a favor talking to them, hell, you're the best thing to happen to them all day!
Anyway, once you get comfortable with that, then that pretty girl? well she's just another person and you've met a million jsut like her, so talking with her is no big deal. There's probably a bunch of guys out there who think she's not that hot and wouldn't get nervous speaking with her, so why should you? and if it doesn't go well, we both know there's million other girls out there who are just as hot. anyway, good luck to ya.