1. Get a spyware and adware removal tool.
I strongly suggest getting Ad-Aware 6.0 located HERE and Spybot - Search & Destroy, located HERE.
Make sure you do updates on these programs when you download them and also before you scan. Running the programs atleast once a week should keep you clean.
2. Have an anti-virus
Your best bet on an A-V is Norton Anti-Virus, which is not free. But if you dont have any A-V and want one, I reccomend AVG Anti-Virus Professional Single Edition 7.0 located HERE.
3. Google is your friend
If youre using Internet Explorer 5.0 or above, than you should definatly have Google Toolbar, which you can download HERE. Itll block about every single popup you come across!
4. DONT OPEN EMAIL ATTACHMENTS
Most attachments contain viruses that can cause some major damage to your computer. Only open attachments if you are sure they dont contain any viruses in them.
5. Run Disk Cleanup every once in a while
This can be found in Start>Programs>Accessories>System Tools>Disk Cleanup. This will clean up temporary internet files that your computer stores
6. Run Disk Defragmenter
This one can be found in Start>Programs>Accessories>System Tools>Disk Defragmenter. This will "organize" your files and give you extra disk space
7. Turn on your windows firewall
Go to Network connections>the connection youre using>properties>advanced> and make sure its checked.
8. Run windows update
Keep your computer up to date. Located HERE
If you have any questions feel free to pm me