What are some precautions against computer viruses?

This is no easy task. I would normally say that they are unavoidable since there are so many on the internet. However, I assume that the best way to avoid Computer Viruses is to be careful as to what you download off the internet. As rudimentary as that may sound, computer viruses can only enter if you allow them to enter. Therefore, be careful. Mcafree isn't a bad defense system either, I suppose you can try that too.