I seem to be getting good responses from my post over on the RPG.net forums abut how to develop a 24 hour RPG.
So I'll repost the outline here.
Set your 24 hour goal as mid-day to mid-day (you'd probably want a weekend for this).
12pm - 2pm: Get your ideas down on scrap paper. What's your game about? What mechanisms do you need to make sure you game is really about that topic? What is the setting? Is it different from other settings? How? Why are you writing this game? I like to divide my scraps into...
"Setting" - pretty self explanatory. It might only take a few lines, it might be a quick page, or it might be developed by the players as they play. Make sure you note this down.
"Character Generation" - What stats or traits do you need? Why do you need them? How will the be important to the game? How do you generate them? Do you have pre-made templates or classes?
"Session Start" - What starts the game happening? Do you start with a simply blurb read out to the player to set the scene, or do you let the players choices set their story's starting point?
"Game Play" - Consider the game mechanisms you need to tell the story you want. Do you need combat mechanisms? Do you want rules for social intrigue? Relationships between characters? Do the rules change under specific circumstances (stress, injury, loss of face)?
"Session End" - What are the character working toward? How do they know once they've reached it?
"Joining Stories together" - Are you interested in campaign play for this game? How do characters evolve?
2pm - 4pm: Go over your notes. Are any parts of the game obviously missing? If this is deliberate, make sure to add a new note to explain why you've specifically avoided certain aspects of the game design. If this isn't deliberate, make a conscious effort to fill in your gaps...use rules from existing games to fill in the pieces if the inspiration doesn't hit right away. While you're doing this, make sure that the various parts of your game make sense compared to one another...do you roll high in this section but roll low in that section...if so, why? Gradually start to pull your pieces together into a coherent document.
4pm - 6pm: Write up a draft set of rules; don't worry about formatting, just get the rules down. This isn't a time for writing up new rules, it's just the time when you get your game's framework in place.
6pm - 8pm: Eat. Take some time away from your project. Watch a TV show, surf some forums, take your mind off it a bit. Then read through your draft set of rules and compare them to your scrap-page ideas.
8pm - 10pm: Solo Playtest. Generate up a character using the rules you've written, do it on a scrap of paper. Did the character generation make sense? If not, get a red pen and make editing notes to your "Character Generation" page. Generate a completely different style of character, re-edit the generation system as necessary (24 hour games are quick and tend to be "rules-lite" it should only take a couple of minutes to create a character). Once you're happy, you'll have a bunch of characters ready for the next stage of the process. Run through a typical scene in the game. Pit two of your characters against one another in various situations using the die rolls (or other mechanisms) you've written on the "Game Play" scrap sheet. Do the rolls make sense? If not, make some changes.
10pm - 12pm: Perspective. Did you find when creating the characters that certain things took more time than others? Did you find that the areas focused on in character generation were also focused on during your play simulations? Were there certain traits that you really didn't use at all? If you see any problems here, now is the time to make some extra changes to the "Character Generation" and "Game Play" sheets. If you aren't using an attribute or trait, why do you have it? If it's just used to derive another stat, why not just work with the other stat?
Do you think combat happens too fast, or too slow? What about social interactions? Maybe this is the whole point of the game. Do you still think that quirky dice mechanism from the beginning is useful? What do you think this adds to the game now that you've played through a couple of sample scenes with it? Make some notes on your various sheets of scrap paper about this.
12pm - 6am: Sleep. Don't underestimate this one. You'll probably have some good ideas still running through your head, and you might not get a full night's sleep while the adrenaline is pumping and the ideas are firing away wildly. But make sure you get some good rest so you can come back to the project with a fresh perspective.
6am - 8am: Get some breakfast, then get to work. Using the framework document you wrote up the previous evening, rewrite anything according to the changes specified in your edited notes. If you've had some epiphanies during your night of sleep, add them into your updated file.
8am - 10am: Retest. With a new version of the rules written up, generate a new pair of characters. If the rules still work in the morning, then you've probably got a solid idea in place. Start to generate a proper character sheet by placing character traits in specific locations on the page. If you generate a couple of characters, make sure to lay them out in different ways. After you've come up with a few ideas for character sheet layout, one should strike you as better than the others (if not, just pick one that you like). With a new batch of characters play through a couple of scenes again, and even try stringing a few scenes together to see how they work as a part of a larger whole. If you've got access to a room-mate or partner, play a scene or two with them and get their feedback. If something is causing problems, consider adding a couple of "Play examples" to your text. Don't make major changes to your game at this point, but consider them for later and add them as new editing notes on your scrap pages.
10am - 12am: Formatting. Generate up a proper character sheet. Go over your game text for spelling errors and grammatical errors. Start at the beginning and work your way through. This isn't the time for making changes to your game mechanisms, it's just about getting your current ideas into a good readable format. Include section headings for "Setting", "Character Generation", "Rules" and anything else that strikes you as important for the game. Pick a font that suits the ideas in the game, especially for your section titles. If you've got some pre-made images that served as inspiration during the process, add them into your file at strategic points (a combat scene, place it near the combat rules...a cool character shot, place it in the character generation section). Give the text one last read through, save it or print it out as a pdf using CutePDF (or something similar).
Your document could end up as a single sheet of paper or it might be up to a dozen pages long (2 pages per section), I certainly wouldn't recommend longer than this. The 24 hour RPG challenge is all about getting good ideas out of your head and placing them into a context where others can play with them.