teasing is good to a point, once they start teasing back, STOP! if you get on that level where both of you tease each other, its not gonna go anywhere, and you will be just friends and she'll never take anything you say seriously. DO NOT MOCK! mocking is unattractive and could actually be hurtful, tease her when she is clumsy by just saying "smooth" or something like that but once you do, laugh with her to make her feel that her being a klutz isn't loosing your attraction.
Be smart and take hints, any guy with two balls should realize they've gone too far.
personally i hate teasing, its a weak approach, but some girls like it, you can tell by just looking at the girl, if she likes to laugh, poke fun, if shes more of the serious type, be smooth and choose you words carefully.