The answer I was looking for will sound very simple and obvious: Make sure the players have a chance to learn everything. This sounds very easy, but how can I make sure that every element you put in an adventure has a reasonable chance to be discovered by the PCs.
- NPCs meant for straight up battle should have a very simple background. They are meant to get their butts beaten up. If you want them to have some piece of information, then they should know that. The PCs don't want to hear about the type of cooking their mother made.
- Extending the above, when writing a back story or "how things got this way", only provide as little information for the GM to understand why things have reached the current state. Avoid spoilers as much as possible.
- Focus on the important and let the GM fill in any blanks. This is one thing I struggle with. I keep trying to cram so much more into my adventures.
- Avoid trying to force your GMing style through the writing. Each GM has their own style and strengths.
- Remember that everything you put in there, should have a reasonable chance of being known to the players. By reasonable, I don't mean DC 50 checks or a random "I look through the third house, four street away." Kind of things.
I take the view of "the players must know everything in this adventure."
Where was I going with this and Game Design you ask?
I took all this to FINALLY get to my point. Anything you do in game design must be experienced. Players must play the game. Others must know what you are talking about.
Otherwise, you do what I call "mental masturbation" where you flatter yourself and think and rehash some really cool concepts that no one else will ever understand. Coming up with awesome ideas for settings/ campaigns/ locations/ games I had so developed in my head that there was no way anyone else could play it.
4e initially spoke of "Points of Light" and that is an awesome concept. Get a basic, overall idea for things, and develop them as you go along. That way, ideas that you don't need, can be dropped and those that work naturally receive more of your time.
And how does this relate to SPX? Quite simply, I have decided to approach the project with this minimalist approach. Present something, expand and use it. Everything else can get a broad stroke definition. "This place is full of elves" is more than enough.
A company who I think has done this very well? Paizo. Golarion is full of holes. So little is defined until an Adventure Path explores it in more details. And even then they left areas for a GM to add to it. Quite simply, this has been brilliant as a strategy, and definitely something to emulate.
Another setting that had this approach - though I do not believe it was by design - was Greyhawk. Outside of a few select countries, most of it was empty wilderness for the GM to populate. I worked mostly on two nations: the County of Urnst and Tusmit, both of which had effectively no details provided for them. Lucky for me, previous triads left me a lot of work. Unfortunately, too much of it was done away from the players. I work to change that.
Looking at Wizards, here we have a very different situation, seeing how their settings, for the most part, have existed for at least a decade (Eberron being the new kid). So the comparison is not quite fair. But still, with each edition, they present re-worked settings and offer adventures for them. Look at Forgotten Realms and Dark Sun for 4e.
Now with SPX, I thought of it with the players being front and center of everything. Simple and focused design limited to what I need, allowing me to change it based on a better, later idea OR expand what I have there. Right now, I have a number of documents totaling over 150 pages of dumped rules, ideas, and an overall idea about the world and its history. Again, I left plenty of holes in there to be able to add more to it later.
So... after all this thinking (often in circle), I realized that this approach was very much like many of the Extreme Programming methods in software development. I could not help but laugh at the idea that I was using my engineering background to write game material.