I got a few tricks up my sleeve I like to use:
1: CCleaner! It's a great tool to clean your computer of the worthless things stored in your drive.
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2: Go to Start > All Programs > Accessories > System Tools > Disk Defragmenter or/and Disk Cleanup
The Defragmenter and the cleanup are great ways to also speed up your computer, the defrag organizes your files so there's less clutter in your drive while the clean up cleans out useless files [though CCleaner does more cleaning than this, its still good to use this tool to get what CCleaner missed].
3:Go to Start > Run [for Windows 7, search run] > type "%temp%" [no quotations] then hit ok
It will bring you to your temporary folder, hit ctrl + A at the same time to highlight it then throw it all in the recycle bin [if there are files still in use, don't delete them!].