Clean your computer on a regular basis. This means keep the harddrive defragmented, remove old software, temporary files, and clean your registry.
CCleaner is a good program for removing the old software, temporary files, and the registry.
Also you should clean your computer’s interior as well. Dust buildup can clog the fans, short out the electronics, and it has a chance of causing a fire. (Just know that for it to get to this point, your computer will have to have gone a number of years without cleaning.)