Among other things the one thing that helps is the game design document (GDD), it is a collection of all the pieces that go into making the game. This is a document created early in the process and is referenced throughout production. It covers all you need to do to develop and market your game. With my latest GDD, I have included marketing and PR efforts since these are handled in house by the folks developing the game.
Another approach would be the Game Pillars which I came across in Michael Futter’s The Gamedev Business Handbook. “These are the foundational elements driving design. All of your decisions should be linked back to one or more of these guiding principles” (Fuller). I found that doing this is very useful for getting a more focused and targeted approach to game development. It really helps with creating the pitch for your game. These are easily remembered, so you don’t have to constantly be looking through your GDD. It summarizes what you are trying to do with the game you are creating and can save valuable time and keep you on point. The larger GDD is helpful to get it all down on paper rather than allowing it to swirl around in my head.
Having these documents has been helpful in keeping me focused on efforts towards creating a finished product.