Things You'll Need
Instructions
Create a system -- a set of rules that dictate what your characters can be, do and have as they play the game. Use the dice to determine the statistics of probability for each action's success or failure. Keep in mind that there need to be conflicts, resolutions, and a clear end goal in order to make the game worth playing. As you play-test the game, this will become clearer and be rewritten multiple times until the playing is smooth, fast, and fun.
Design a setting for your characters. This is the world they live in, which dictates what actions are possible or not. In a fantasy world, it is unlikely your characters will be shooting ray guns at one another. In a world with physics matching the real world, humans cannot fly. The storytelling of the game comes to life with a richly detailed setting.
Set up a scenario for your players. The simpler the scenario, the faster the game will play. For example, conquering the world will lead to a long game, but traveling from one castle to another to rescue the princess might be over quickly. Using dice to calculate the odds of success, each character meets conflicts, resolves them, and moves on to the next step.