1) If you ever get a virus on your computer: Format the hard drive and reload everything clean from scratch. Do not bother trying to "clean" your computer, it's impossible to garantee it will be 100% "clean" afterwards. Rootkits make that impossible to garantee. Just wipe and reload it.
2) Always install a second hard drive or attach a USB external drive to store all of your working files (documents, pictures, music, movies, etc.)
3) If you have kids, get them a separate computer. Don't let them use yours. Don't join their computer to any shared environment (workgroup, domain or home group, etc.)
4) If you use a wireless network, lock it down. Don't ever use it in "out of the box" configuration.
5) Use at least two (2) web browsers enough to be familiar with them.