|Use disk clean up feature.|
Clean out your browser weekly (cookies, history, temp files).
Uninstall programs you do not use.
Delete old emails.
Delete old files you do not need anymore.
If desktop add additional hard drive for more room and move most files to the new drive; If laptop get external hard drive and move seldom needed files to an archive folder system on the external HD. You should have at least 15% free space for a hard drive to operate properly.
Repeat disk clean up and do a defrag.
You have to be a little bit crazy to keep you from going insane.