How to prune a snake plant?
Snake plants really don't need that much attention, and cutting the leaves can actually damage them (and sometimes cause them to die), so you should really only prune if or when the tops of the leaves become brown and wither. I only cut mine just a tiny bit above where it turned brown, being careful to make a very clean cut so that you don't end up with any "strings." The leaf will heal up that edge on its own (as long as you're caring properly for the plant).
This article contains more information about caring for Snake Plants: