Go see her as much as you can. Flirt back with her.
When it feels right ask her out. By this time you should know her well and will have a good idea for a great date.
Originally posted by Umbrax
If you feel like you don't know what to say then you probably need to build up some self confidence.
A safe route to take is to shut up and listen to her and ask questions about her.
She obviously finds you attractive. That is half the battle.