SAY A PLAYFUL BANTER LINE
Banter is basically "content-free conversation." Only use memorized banter lines when you can't think of one on the fly.
Try these:
"Hey! You're cute! You can help me pick up chicks!"
"I can already tell that you're trouble!"
"You're not fooling me! I see those devil horns hidden under your halo!"
"Did you come all the way over here just to flirt with me?"
Has she smiled yet? Even once?