1. Never spam and never reply to spam emails.
2. Never access sensitive websites(paypal, ebay, bank accounts…) using links included in the emails or from public computers.
3. For any popular commercial application there is FREE and equally good alternative. More on it in Fully loaded windows at 0$ cost.
4. Regularly backup important data and if possible keep it on non-logical partiton to avoid loss in case your hard-drive fails.
5. Always keep your Firewall on and regularly update your Antivirus, Spyware and Operating System.
6. Never trust flashy ads or pop-ups stating that your PC is infected or something similar.
7. When you need a specialist go to a credible source. Anyone with basic HTML knowledge can launch a good-looking website and publish whatever nonsense s/he wants.
9. RSS and all these feedreader stuff rulez! Use it…
10. If you aren’t using firefox that’s only because you fail to realize its potential. Try again and have a better look at so called extensions