Be forward! Dont hide anything about what you are thinking and dont think you have to impress her... even more so do not think you have to handle her with kid gloves and be worried about making her mad/not like you... it is the worst thing you could do.
Be EXTREMELY normal like you would be around your parents or something... if she starts to give you S**t tests (asks you dumb questions, suggests that you are something, etc) play games with it, ignore it, or just act crazy over the top cocky about it with a smile on your face. I am 25 and look 16, so when I talk to girls older than me, I get the "you look so young" line alot... I can blow this test out 99/100 times now with lines like "well, I am old enough girl!" or "you are right, I thought you looked younger from over there, now, not so much".
Go over the top to show how much fun you are, and how much fun you have all the time, and she will have basically no choice not to like hanging out with you. DONT take her seriously!
Some other fun tips if you get stuck in conversations that are lame...
Say you are talking about something and she says some sorta suggestive word in a completely boring sentance... make some wild "suggestive" comments on it like "we have only known eachother for a few weeks and you are already thinking about that?", or "what kind of guy do you think I am to be talking like that around me?"
Also, never directly answer a direct question unless the answer is no. respond with another question, or some sly player remarks, or just stare her down followed by a goofy smile.