just talk to her. dont stare at her. thats just creepy.
And, usually, just say hi. people say to use all these pickup lines and stuff, but honestly, if you want to talk to a girl (or anyonee!) just walk up and say hi, my name is _____, whats yours?
so offer to do things take her out or ask if she wants to hang out i really think you should like let her do the more talking get to know her and ask open questions.
ps. have the time to figure her out before making a move