Make sure it still makes sense!

Now that you know (or at least have a clue about) who is hopefully going to play your game (and why) and what your game is going to be about, and how it's meant to be played, what achievements / rewards are possible etc etc, it's time to go back to the drawing board and make sure that the original design makes sense. Does the game follow a logical progression, is what you have to do inline with your target markets philiosphy and beliefs. Do any elements of the design deviate from the targets current world view (if so why? - are you deliberatly trying to push boundaries, models of thought?).

Now is a perfect time to go back and work out any kinks in the design, start to flesh out the game world, fill in the back story (if appropriate), design the main characters (what they do, how they act, what is their reasoning etc etc), and set the scene and the style of the game.

Now I'm not saying ALL games have to have a complex back story, depending on the type and genre of the game all this extra effort may be counter productive (who want's to wade through a ten page intro just so they can play space invaders or pacman), but it is important that the game (and all of it's elements) should form a solid cohesive structure, if not for the sack of beliveability (or to help create a total suspension of disbelief) then at least so that the final build be presented in a polished professional way where by the finished product be greater than the sum of it's parts!