Hi,
Main two virus attacks are web and removable devices. AVG is not bad if it is updated frequently, but I advise you to pay for a Kasparsky for further protection. But in all cases avoid visitng untrusted web sites or using p2p applications like limewire or emule. For the removable devices, never copy any file from or to prior for scanning it. A trick i use even before openning a flash memory is to open cmd and write f: or device letter, then write dir/ah that will provide you with the hidden files and folders. I then delete every thing i find not proper using : del zzz.exe /a/f
this would minimize the chance but you will need the protection any way