1. First of all you need to disable autoplay option from your computer. If you don't know how to disable autoplay then go here . Once you disable your autoplay then pendrives having viruses will not attack your pc automatically.
2. Never double click on any new drive on your computer. When you connect a pendrive or any kind of drive in your computer then right click on it and then Explore.
3.When you are using internet, never try to click on any untrusted page. How will I know it is trusted or not??
The answer is you will know this when you use internet for a long time. But for begginers I will suggest not to browse pornographic sites or ads seeing porn.
4. Frequently check your e-mail and check if there is any spam or not. If you find any spam then don't open it and just delete.
5. Try to use genuine version of your operating system. It's virus protection is higher then pirated. Who use microsoft's operating system, I will suggest them to use Windows 7. It's virus protection is very very powerful then windows xp.
6. If you want to download any software then you must download it from well known sources.
7. Most of the time when virus attack our computer they affect softwares saved in our pc. So if you zip them then they will never be affected by virus even if your pc is full of viruses.
If you follow these seven ways to protect virus without antivirus then your pc will be virus free. Try to follow these tips.