I've never had a virus or malware get onto my computer. Here's how:
1) Use a firewall software app that is also a computer monitor such as ZoneAlarm (which is free).
You may say: "You probably have malware on your computer and not even know it." And I say, even if that's true, my firewall monitor lets me know if an unknown application is trying to access (hijack) my network connection without my knowledge -- and it lets me give it permission or not.
2) Always assume something is a scam until it proves it isn't a scam. If you're unsure, do a search for it with the word "review" or "scam".
3) If there's a link that is wants you to click it, don't click it. If there's a link that's just sitting there and its address is the same as what it's claiming to be (on the mouseover hover), it's probably OK. But be sure.
4) Don't click on any email link ever. Even if it's from a source that you recognize. If it's from a legitimate business it will have come through a third party e-business site that will collect your information. If it's from a friend, it may have embedded information in the link that can identify you personally or it may be a virus email using your friend's address as a host. You can never be sure. If you can't duplicate the link exactly, such as with an awesome Fail video your friend wants you to see, search for it yourself using Google or Yahoo or Bing or Youtube. If your friend found it somehow, chances are you'll be able to also.
My bank does not send emails with links in it. It sends a notice that I should manually go to the bank's website and log in to retrieve any information that I might need. This is excellent advice.
4a) If an email prompts you to navigate to a link, type the address into your browser yourself and navigate from there.
You may say: "You're too paranoid" or "That's too much trouble". Both of these are probably true. But results don't lie.