Storyboarding

One of the best ways to see a game is to storyboard it — to create a sequence of drawings that show the levels of the game or the different scenes and goals. Each storyboard should include a paragraph or two to describe what is going on. Figure 1 depicts a basic storyboard for an imaginary shoot-'em-up game.

Figure 1: A typical game storyboard.

As you can see, the storyboard has six frames; each frame represents a different level of the game, and the final frame is the goal. Notice that the storyboards are sketched and messy. Storyboard sketches are used only for brainstorming and for getting down on paper the general flow of the game.

Read more: http://www.dummies.com/how-to/content/designing-video-games.html#ixzz1QbUgZ8k2