Do not go onto random websites, if you do want to, use http://safeweb.norton.com/ to check if the website is safe to go onto.
Do not give personal information on websites that is untrusted and not well popular sites (these personal information would include bank details, address, telephone number etc), something like google, yahoo and youtube is where you can give personal information to.
Do not click onto adverts, many of these can install an adware on your computer without you knowing. Or, they can lead you to a website that gives you a virus.
Use a browser with good security, im not sure what browser has the best security, but i would say just stick with Internet Explorer.
Use a good anti virus, do not use free anti virus if you want good protection, as they have low detection rate. I would suggest buying norton, mcafee etc.
Even though you have an anti virus, its best to install malwarebytes as well. This is good for a secondary anti virus when your primary anti virus has failed to protect you.
There have been some cases on MSN when your friend would send you message with a link, do not click onto this, it will give you a virus and give you the same problem. Also on facebook, there have been many of these wall post which is something on the terms of "OMG you would not believe how DIRTY this girl is", do not click onto these, clicking onto these will results in it being posted onto your wall, and in some cases give you a virus.
Do not open emails from people you do not know, these can be spam or viruses. Only open emails from friends, and emails from website that ask you to activate your account because you have signed up for their website.
That should be all.