it's simple, here's some basics... always smell good, smile a lot, look at their eyes(don't stare), don't talk too much, but use their name often. have your whole body face them while talking. don't worry about active flirting yet, you'll learn.

there are a few surefire ways to tell if a girl is into you, just learn them and keep them in mind. girls tend to play with their hair, look you up and down while talking to you, and open their legs toward you(not necessarily spread eagle, just not closed), plus all the stuff i talked about above - except not talking much, talking is natural for girls :P just focus less on the conversation and more on external signals, and you'll notice.