I think a decent ad-blocker and some common sense is good enough for 99.9% of us. Block ads, and if something doesn't 'seem' right, then don't open or install it. Both Windows and OS X now have pretty damn good inherent protection, you almost have to completely allow something in to get 'infected'.
Basically, don't believe internet ads, and don't install anything you didn't specifically ask for. If something asks you to install it it is likely no good.