Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live - Martin Golding

This needs to be stuck up on the wall somewhere within site of all the developers. In the past we've had posters explaining KISS (Keep It Simple, Stupid) and had rules such as the 2am rule. Make sure your code makes enough sense so that if things go wrong at 2am. In your sleep deprieved state loaded with cafine you'd understand what to fix.