Well, the old community cure for one-itis was to go out and try and bang as many girls as possible. I've never really had one-itis but, I figure, time heals all right?
I wish I knew. There is a gal I have my eye on, but it will never happen. With distance, and some other factors.
The only thing that is going to help you get your mind off a girl is time. Sometimes lots of time. Sometimes not so much. Spend your time doing something you enjoy and focus on that.
After a break up or rejection, I used to try to stay positive and focused and I used to put a lot of energy into trying to prove to myself and other people that I was ready to move on. I accomplished nothing in this except wearing myself out and prolonging the pain. With the failure of my old approach, I discovered a new method: become totally apathetic for a week or so, stop caring about anything, including your health, hygeine, friends, family and woman. Get drunk, binge eat, spend ridiculous amounts of time on the internet, turn up late for work, stop watching the news, play video games. Within 7-10 days you'll get bored and you'll want to start living again, only your fixation on this woman will have miraculously disappeared. Maybe when you shut down your cognitive faculties for a little while it resets you and puts everything in perspective. I don't know if this method would work for everybody, and it does sound ridiculous, but its been working for me.