1. Install a good antivirus. Free or Paid is good, but dont used cracked or pirated versions.
2. Install real-time anti-spyware protection
3. Update your Anti-virus programs daily.
4. Perform scans on your computer daily.
5. Disable auto run to prevent infection from pen drives.
6. Disable image previews if using Outlook
7. Use good anti-virus which has browser plugins and scans all URL's for malacious content.
8. Use Hardware based Firewall.
9. Don’t click on any mail links or attachments from unknown sources or malacious users.
10. Never download software from third-party sites. Download from original website. Don’t use cracks or keygens which may be a virus/Trojan itself.