Flirting is fun, and that's what your main focus should be Col, have fun.
Girls (especially pretty ones) get complimented/commented on/hit on by guys regularly, they can be desensitized to accepting any typical approach. If you want to get in you have to be different, don't force the relationship or come on too strong, just have a good time with her and focus on how happy it makes you and tell her that.
If you go in with a clear intent that you want to get with her -which can be okay- you will automatically be grouped together with all the other guys that are blatantly trying (and failing) to get with her, just hanging around as a happy friend will get you closer and also keep you out of that category of strongarm hookups.
A little flirting along the way helps, just don't push it too far or focus your comments on her appearance, she's probably heard it enough already from every other guy.