Be romantic, although you shouldn't be creepy. Try becoming friends with her.
I heard somewhere that about 10 seconds into a conversation a girl knows if she may like a guy. This is probably subconscious though. Once you become her friend, start texting her and eventually ask her on a date!
You could do little romantic (but not overboard) "hints" to show her that you like her before this. Try to avoid getting friend zoned. Make sure you don't do any of these things (besides befriending her) if she's dating somebody. That will tick her off.