This is an amazing essay (at least I thought so) from Gamasutra on how to map out your game so as to see how the mechanics interact with each other, the hope being that it will allow game designers to begin to refine the game design process into more of a science. It's written by Daniel Cook, who writes a superb game design blog at www.lostgarden.com
http://www.gamasutra.com/view/feature/129948/the_chemistry_of_game_desig...