A hard drive fills up when you install too many programs, and save too many files to the drive.
This is true for both local hard drives in a users PC, and network shares.
Too reduce the amount of drive space used, consider the following:
How many backup copies of a file do you need?
Do I need to store a copy of a file that is on the network on my PC?
How many screen-savers and wall-papers do I need?
How many fonts do I actually use?
Should users be allowed to store MP3 and other media files on their PCs?
Same for user installed software. should it be allowed?
How many different programs that perform similar tasks should be allowed on a users PC?
IE / Netscape / Mozilla
MS Office / Corel Suite / Star Office
Image editors
CADD software
Things that users can do to help free up space on their drives:
Empty the Recycle Bin.
Clear your temporary Internet files.
Delete any un-needed messages from your e-mail software.
Scan images to be used in documents too a 'reasonable' size.
You do not need 1200*1200 DPI resolution for a picture that you are going to shrink 75% to fit it into your report.
For MS Word, clear the document history after the final revision.
Shut down your PC properlyto avoid creating chkdsk files when scandisk runs at startup.
This covers most of the basics. I am sure you will get additional ideas from the list, and other peers.
Chas