Computers are really addictive. You can talk to friends, search for things, or play games. However, spending too much time on the computer means you miss out on other things in life.

Ask yourself how much time you spend on the computer. Is this excess time interfering with your social, academic, family, or religious life?
Set a certain time to be on the computer. Even if it is hard, limit yourself to around two hours a day.
Get interested in a sport or other activity you can do with friends, so you won't have to be IMing them instead. Face to face talking is much better anyway.
Realize that it is not the end of the world if you are not able to check your email every single second. In the event of a truly important or timely matter, people will usually contact you via telephone or in person.
Close all your unnecessary accounts -- (MySpace, Runescape, Facebook, etc.).
Get out of the house. Go to a local coffee shop or even the mall for a change of pace.
* Setting a certain time for yourself for computer time it isn't always easy. Choose two or three hours a day but be careful on how you space them. Having them too far apart can be torture, but having them too close together gives you little time to do anything in between. (Feel free to have certain schedules for certain days of the week.)

* Don't start to freak out the first day when you stop being on the computer. Don't just quit, that will torture yourself more, spend some time on schoolwork you've been delaying or go for a run or bike ride with a friend or two, distract yourself.