SP1,
Take my advice and I promise you this will become easier.
1. Create a state of genuine curiosity in yourself, then approach. Your goal should just be to get to know if this is the girl you want to take to bed. Be playful.
2. Have two, no more than three, openers. Practice them, practice them, practice them. Oh, by the way, did I mention you should practice them like an actor practices his lines, so that they flow naturally from you. That way, when you observe the three second rule, you'll have something to say to her. I'm not going to tell you my three, you'll decide for yourself, but I have one opinion, one direct, and one put-on (see Ross Jeffries Gold Walk-ups for more info on this).