You can never underestimate the power of humor with girls (if you question this concept at all, do a search of male comedians online and see how many of them are dating gorgeous models). Make her laugh and you'll be one step closer to landing her heart.
When you're together, try to be at your wittiest. Have some material prepared ahead of time: Try some cute jokes or one-liners that you can throw into the conversation as casually as if you'd thought them up on the spot. (Just try them out first on a friend to make sure they don't bomb.)
Keep her laughing by sending her funny e-mails or links to hilarious videos, and add your own clever comments. Post cute jokes or notes on her Facebook page.
When the two of you hang out, take her to places where you both can have a good laugh. Get tickets for her favorite comedian or go on a bumper car ride at an amusement park.
She'll be having so much fun that she might start to look at you in a whole new light.