Cleaning up yout computer

What is the right way to clean up your PC to make it run faster again. I notice that after time my mail and internet slow down. It gets to a point where it so bad I have to reformat my hard drive and start over to make it better again. What is the best way to clean up my PC without having to reformat?

Disk cleanup in system tools is a good place to start. When I defrag my hard drive I boot up in safe mode first. Defrag will run faster and I go can clean out anything left it my temp folders. Cleaning out your INTERNET history may speed things up too.