1. Always have a good anti-virus if you can not afford to buy one go with avast or avg free edition.
2. Always have a good firewall. Some good ones are COMODO free, Zone Alarm free and (COMODO allows you to see what files do when their ran like if they inject into another process or if they open another file).
3. Good anti-spywares are a must. Some good ones are Spybot Search and Destroy, Ad-aware se, and AVG Anti-Spyware (avg anti-spyware is a combination between another old anti-spyware company and avg.
4. Its always good to have good tools that help detect possible undetected viruses as well. Such as Hijackthis, runonce and autorun.
5. Rootkits are another major issue rootkits can hide a detected virus from almost any anti-virus as long as the rootkit is undetected. Some good tools are avg's anti-rootkit, unhackme, RootKit Unhooker, and Icesword.
6. Security holes. For those of you who do not know microsoft updates will keep your programs on your computer up to date. Its best to do so because old software is vulnerable to security holes that have been fixed in new versions.
7. Last but not least system recovery disks can be a life saver for when a virus destroys your Master Boot Record. I recommend to every to go and buy one if you did not get one with your computer.
Now enjoy a safer and less scary online experience 🙂