How can I make an impression on her?

ok i'll fill you in on the whole story. there's this certain female that i really like. she is a freshman, and i'm a junior. i am real good friends with her sister, who is in my grade. i already took the initiative by introducing myself to her, but i dont have any cles with her so i dont see her a whole lot. but my dilemna is this: we say hey to each other in the hall and stuff, but how can i really make an impression on her and get her to be more attracted to me? and im not all for the straightforward approach. i'd rather be somewhat subtle. so what do yall suggest i do?