Well, just say hi. Start off with hi, maybe make something up, like 'Do you know where . . ' or something like that.
If you'd prefer 'more than friends', I'd say compliment her at first. I am a girl, and no matter who said it, it's nice being complimented, or asked out. Lots of people are scared people will say no, but they need to remember, being asked out is a compliment, and they worst that can happen is that they say no and it'll be a bit awkward for a while.
Just say hi, strike up a conversation, and then everything is a lot easier after that.