My best advice:
Start doing things you like to do, whatever that is. It might be theater, choir, sports, year book, newspaper, etc.
Just start doing it. You'll find other people that share your interest. Some of them will be girls. Just be yourself and be FRIENDS with these PEOPLE (girls). You might be surprised what happens from there.
People can sense desperation and they generally shy away from it. If you come across as "Desperately Seeking Girlfriend" they will know. But if you are just being a friend, well, this is how all good relationships start.
Good luck to you
