GENERAL COMPUTER MAINTENANCE TIPS:

Keep all of your working files in one folder. The My Documents folder is offered by Windows expressly for this purpose. The benefits of keeping all your files in one place are multiple. One, you know where all your files are, two, it's easy to back them all up at once, and three, your machine will run faster.
Don't put your personal files on the root of the C: drive. If you store a large number of files in the root folder, you could corrupt your disk file table which could lead to a "NTLDR is missing" error message when you boot the computer. Very bad. If you have personal files on the C: drive now, move them to the My Documents folder.
Uninstall programs that you are not using. But don’t just delete the program. Remove it correctly so you won’t cause Windows errors. Go to Start, Control Panel, Add or Remove Programs. Find the program you want to remove in the list, and click the Remove button.
If you download a zip file and expand it, delete the original zip file when you are done.
If you aren’t already using one, get a good surge protector and plug your computer into it.
Don't accept software or downloads for which you didn’t ask. Delete any suspicious email without opening it. And even if the email came from your best friend, don't open any email attachments with the following extensions: * .exe, .com, .vbs, .bat, .mdb, .reg, and .js

WEEKLY COMPUTER MAINTENANCE TIPS:

Make sure your anti-virus and anti-spyware programs have been updated with the latest definitions, and run a full scan from both programs.
Reboot your computer. (If you shutdown your computer each night, disregard this tip). If you leave your computer on all the time, definitely do this. It will reset the RAM, and your computer will run much better and faster.