Below is 11 tips for you.
1. Update/patch ALL your software every now and then!
2. Check/adjust ALL your settings so they are safe, since they AREN'T by default!
3. Use firewall, like ZoneAlarm to control what goes in and out from your computer!
4. Use good passwords: at least 13marks long, containing both letters and numbers. Remember to change your password every few months at least and don't ever use the same password in two places!
5. Get a good antivirus program: NOD32, F-Secure, AVG or Norton Antivirus and keep it updated!
6. Don't open or execute files that you are not 100% sure are absolutely safe nomatter where or how you get them.
7. Wipe your history files (like cookies, internet history and temporary files, etc.), logs and personal files, with specific wiping program (like Eraser) instead of just deleting them.
8. Use encryption to enhance your privacy! Use encrypted email (like Hushmail or Ziplip), www-surfing and encrypt sensitive files on your computer (PGP).
9. When you are finished using some internet-based service like email, sign out of it rather than just closing your browser! Also, when you leave your computer, make sure that none of such programs or connections are left open that someone could abuse. In WindowsNT/2k/XP, press Windowskey+L to lock the workstation.
10. Don't use public computers for anything you need to type in your logins, they usually have Trojan horses that capture your passwords.
11. Make backups and store them in safe place! Easiest way to do a total-backup is to make an "Image" of your hard drive or partition and store it on safe location, but floppies will usually be just fine for storing documents, etc.