If you have a huge crush on someone, there may come a day when you realise that it's never going to happen for the two of you. You have two options at this stage: you could sit around and mope forever, or you could just get over your crush and move on with your life. The latter is not only the better option, it is also inevitable. You are bound to get over your crush someday, so it behoves you to take some steps to get over her now rather than sit around miserable and wait for it to happen later.
Stop seeing your crush. This doesn't have to be forever and you may well be friends in the future, but as long as you see him you are not going to be able to get rid of your feelings for him. So, avoid places where you know you'll run into him, hide him from social networking sites and don't call him. This will help you realise that he's not really as special as you've fantasised him to be.
Remember that crushes are fantasies. Everybody has good qualities and everybody has irritating qualities. If, however, you have a crush on somebody without dating them you have effectively shielded yourself from her irritating qualities, which makes her that much more attractive to you. Remember that she's human, and has just as many negative qualities as anyone else, and you'll quickly start to forget that you had a crush on her.
Avoid talking about him. If you talk about him, you'll contribute to the fantasy.
Focus on yourself. Go to the gym, buy some new clothes, take an extra-curricular class and generally improve who you are by learning new skills. This will help you refocus your energy internally rather than externally, which will help you get over your crush as a crush is the ultimate in external energy focus.
Talk to new people. This can be anyone, but if you talk to more people, exchanging observations and asking how their days were, you will start to realise that everyone's friendly and there is plenty of potential for new crushes in your future.