Here's some great tips for keeping your system clean.
1) Never use Microsoft's Internet Explorer to browse the web. Use anything else and you'll avoid a large chunk of problems. Use Firefox (It'll use your old bookmarks!) and throw on some ad-blocking add-ons to be safe. Accidentally clicking on ads is the easiest way to end up with a virus.
2) Keep your Windows up to date with patches and security fixes.
3) Use a good spyware/malware/adware blocker and remover. Spybot Search and Destroy , or Malwarebytes Anti-Malware are two excellent freebies. Check your system once a week minimum.
4) Use a good anti-virus program. Windows Defender is supposed to be great but I use AVAST! (it's free!) and it kicks ass just fine. Check your system once a week to be safe.
5) Use Dogpile or some other meta-search site: it'll run your search through 3-4 different search engines at once with the same accuracy as the hosting search engines.
6) Be aware that some viruses can spread via Thumb/Jump/Mini/USB drives. Just like sex, if you don't know where it's been, you might want to think twice about plugging into it.
I hope this helps, just try not to send in any bad turns!