When teaching my game design classes, I often see students struggle when I ask them to summarize their game ideas. It can take very long times until they have made up their minds, and very often, crucial parts of their game description will be missing. To find a solution to this problem, I developed this thing for them: My Game (In One Long Sentence). It's a bit like an elevator pitch, I'd say.
Anyway, this is how it looks like:
And this manual explains how you deal with the details:
I have no idea how you will react to this, but I'd be happy if you comment on it. Maybe it misses something? Maybe the manual needs to be written better? Just toss in your two cents; it'll be highly appreciated... and if you're ever going to use it: have fun!