Avoid installing unnecessary software in your PC and uninstall the software that are not used , it will increase the speed of your system.
Defragment Your disk one time per week .
Use a trusted and reliable antivirus and update it regularly .Don’t use more than one antivirus , it will slow your PC performance.
You can clear your system from unused and unnecessary files by doing this following command regularly:
1.Go to start-> Run. Write %temp% .Then click Ok .Many files will appear .Delete these files. It will increase the space of your system .
2.Go to start-> Run. Write temp .Then click Ok .Many files will appear .Delete these files.
3.Similarly Go to start-> Run. Write temp .Then click Ok .Many files will appear.Delete these files.
Keep at least 15% space of each drive Empty . It will increase your PC speed.
When insert pen drive or any other portable drive check it properly with update antivirus.
Try to avoid scam mail and be aware about browsing risky site (Specially porn site ;many of them may harm your computer by serious virus attacking).
Keep your computer in a dust free clean environment.
Do not run too many programs at a time if not necessary .It will create pressure on your system.Never open your pen drive by double click. Open it from explorer .