Best answer as chosen by user elliehowe: Maintain Your PC
It's ongoing... Get in the habit of-
1. Keeping your antivirus up-to-date and scan your PC.
2. Use Disk Cleanup.
3. Clear cookies.
4. Use Windows Task Manager to see what processes are hogging the CPU. You can research the process name using your search engine to see if it's needed. If it's not needed- kill it!
5. Review your System Configuration Startup (msconfig) and deactivate any unwanted startups.
6. Defrag your drive.
7. SpyBot SD is a great tool. The application is updated every Wednesday. You would need to download the updates, immunize, and run the Search & Destroy.
This should get you started...