I’ve come across a very interesting list of rules for game design. There’s a group of people gathering rules to help newcoming game designers (and I’m sure some seasoned ones!) to cope with the weight of designing a fun, fun game.
They have gathered 112 rules with different domains. I’ll link to the site now: http://www.finitearts.com/Pages/400page.html ; if you’re interested in designing a game, please check it out. They are very smart people!