Step 1: Spot the Girl and Talk to Her
Walk up to her and just say "Hello" if she says "Hello" then you may continue talking to her.
Ask her what her name is. If she tells you to go away, then she is not interested. If she tells you her name then you may continue.
Ask her a couple of questions. It really helps in getting to know her and making your self look like you really want to talk to her. Also, throw in a couple comments about your self too. For example: if she says she like ice-cream and you do too, tell her that.
Be funny!!! Girls like funny guys no matter what they look like.
Remember to act nice to her. Girls like it when you talk to them like they are a human being and not just an alien from Mars.
Also it is IMPERATIVE that you remember to be confident. Girls are attracted to confidence.
Don't be afraid to use cheesy lines so long as you say them in a sarcastic tone. That way she knows that you are just saying them to seem funny, and most girls will find it funny and you will get some laughs.
If you only take away one thing from this step let it be this: It's not what you say or how you say it, it's having the guts to say something at all.