NOTE
The length of your GDD is going to be dictated by the complexity of your game. A GDD for a mobile game might only need a 30 page document. A console game might require a document over 300 pages. Game designers have struggled with just how long a game design document should be. There is a movement within the game development community to keep the game design document as short as possible, for a variety of reasons. In the end, I believe a GDD should be just long enough to accurately describe what is going on in the game. However, don’t let that intimidate you. The other documents—the one-sheet, the ten-pager, and the beat chart—are all steps to help you reach your goal of a completed GDD.
Speaking of the basics, you should make sure your document is readable. I’m not just talking about using proper grammar or using correct spelling and punctuation—all of which are very important...