I was always told that if someone couldn't tell what your code was doing by glancing at it, you'd done it wrong and should re-write it.

I know that's absurd in practice, we don't always have the time but I've always used comments as a last resort.

If I need to comment code to make it understandable at a glance, so be it but I'd rather avoid them all together and rewrite until it's clear enough without them.