When I'm board in Globle Studies I do. Then I go to Science class, blow my teacher away because I'm the only studient who can made games. Then take it too math, get help on some of my math for the game. Then go to Activity peroid, sleep & go home.
I draw the charachters/objects to paper usually when starting to make a game.
Beware, be alert, prepare to defend yourself, or just run for your lives(!), because
JarmoNator has entered the building... (see avatar)
that dark human beast is almost unstoppable, invincible and totally gone CRAZY!
Typically as a "design document" I will make a mock screenshot of the game in action... then build it from there. As long as it ends up looking like/better than the screenshot then I must be doin' OK. The only time I ever "write" stuff down is when there is character dialogue or storyline stuff involved... that way I can read it 24 hours after it was written to see how stupid it is and fix it.
Having said that, there is a LOOOOOOOOONG term project I have been working on with a design document that would sink a battleship or 5. Check it out if you want... it's forum based so you might have to sign up to view it, but it's all nicely organised etc etc and all "posts" are on topic.
http://eclipse.massimmolation.net/