I have a few things that I personally use and recommend to help keep your computer safe and secure from viruses and other bad things around the internet.
To start with I will talk about anti viruses (av). There are many av programs out there, some charge monthly or yearly payments and some are free.
For the average person, I believe free av protection should be more than enough.
I personally use and endorse Avast!
They offer a free version as well as paid versions. Most people should be well covered using the free version which can be download from their website http://www.avast.com/free-antivirus-download
Another way to protect ones self is by using a secure dns when accessing the internet.
DNS is what your computer uses to find the real address of Google.com. Just like if you said I am going home, you translate home into your adress, a dns server translates google.com into an ip address that your computer can connect to.
There are many free and paid dns services that you can use to keep your urls safe and clean. Google, OpenDNS, and now Symantic(currently in a public beta) are some of the providers of secure DNS solutions.
A more advanced way to keep your computer safe is by using a "Sandbox". A sandbox on your computer allows you to run an application in a protected memory space so that none of your actual files are modified.
The program I use for this is called Sandboxie.
This program allows you to run a program such as your web browser in a sandbox. It makes a temporary copy of all the files that the program calls for so when if the program tries to modify any files it only changes the temporary copies causing no damage to your computer.