The first thing that you need to do is to remove everything that is about your crush from your room and therefore your eye-sight. If you have any of their posters, DVDs or CDs, magazines with their photos, etc. in your room, collect them and put them all in a box. Seal the box with tape and either put them under your bed, in your closet, or simply put them in the store-room so that you are not tempted to open the box. If you have their picture set as wallpaper on your computer, replace it with something else.
If you hear that their new album or film has arrived in the market and theatre respectively, do not give in to your temptation to purchase the album or watch the film. Distract yourself with some other music or film instead.
Do not buy any magazine that has their picture in them. Looking at their picture will only make you weak and eventually make you give in to your temptation to start obsessing over them again.
Do not discuss your famous crush with your friends. If they start talking about that person, change the topic. Let your friends know that you are trying to get over your crush. They will definitely help you out.
There are bound to be things that you have begun to associate with your famous crush and thus remind you of them. Try hard to relate these things with other people so that you go not find yourself being reminded of your crush every time you come across those things.
Start paying attention to real people. If you are a girl, you will definitely have cute guys around you. Think about one whom you find the cutest. If you are a guy, focus on the girls around you. You are bound to find one who can make you feel really happy and complete.