[youtube]http://www.youtube.com/watch?v=_ZlZryEKdXE[/youtube]
These guys give good advice. Basically, go up to her, and say something. It works. You just go up to her (or really any person you'd like to meet) and talk to her with confidence. If she stays to talk, she'll give you her number when you ask. If she doesn't, she can go fuck herself, and you don't need to feel bad about anything. If she wants to stop, but is actually in a rush, ask for her number.
Now where to go once you've gotten her number is a whole different ball game.
Edit: Apparently I suck at youtube tags so http://www.youtube.com/watch?v=_ZlZryEKdXE