The method I use has avoided virus infections since 1987.
I use a cheaply bought ($50 used laptop) computer for financial transactions only. So there are only 4 web sites I visit on this computer, all large corporations. I never go to any other sites, and never read emails on this computer. Only way I can get infected is if those 4 multi-Billion outfits get infected without knowing it. Also my visiting those 4 sites is very infrequent, only on as needed basis.
For all other work, like paying utility bills, emails, surfing the net, etc, I use a fairly new computer. I do not use any anti-virus software on this. If I get infected (only adware so far) by a virus, or when computer becomes sluggish, I simply re-format the hard drive and reload fresh copy of windows from CD. That kills every virus and disease. Then it is 30 more minutes to reload software and backed up data.
Both computers run fast without any anti-virus bogging it down.
I should add to above post that first thing I did on the used laptop was format the hard drive and load a fresh copy of windows.