I have clamav installed, but only run it sporadically during attacks of paranoia. The only thing it’s ever found was a Windows virus in an old email attachment among some files that had come from a Windows box.

The main thing you need to do to avoid viruses is avoid running untrusted code, which means, among other things, using paranoid browser settings. Linux tends to have fewer random holes where script execution environments ooze into places where they really shouldn’t be, although even Windows isn’t quite as bad about that as it was twenty-five years ago.