Try not to think of them as "girls" when you're around them, but instead, your fellow human being.
Don't be a creep/freak/sicko or whateverthefuck unless you know for certain they're down for whatever you're playing,
Most chicks don't want sex after the 3rd conversation, expect to be building a friendship for minimum 6 months unless she's desperate or you're hot shit.
Try not to be pushy, just talk to them as you would a male friend.
TL;DR act like a human.