Leave yourself room for later. If there’s anything I’ve learned from doing lots of worldbuilding—for my own linear fiction and for the collaborative fiction of RPGs—it’s that trying to fill every last nook and cranny of a setting is a daunting task. And actually filling up everything is choking, stifling. Don’t fill up everything. It leaves no room for the future, and it leaves no room for anyone else.
I wrote about this in passing in my World Seeds’ back matter (see also Whimsy’s Throne). I want those to be more than just a kernel of an idea, so each also has a section that outlines a quick how-to for using the Seeds themselves, and offers training wheels for storytellers still growing into their own skill.
My words in my World Seed project, from the Example Answers section and the Turning Answers Into Prep Elements section:
“Write your answers down, and be sloppy about it. Leave some details undecided, leave problems unresolved. A painting begins with a rough sketch, and these answers are just a skeleton to build on later. You can flesh out the details further after you’ve put some words down in front of you (or imagined them in your head, or however your brain works).
Your first answers may disagree with later ones. Just keep going. When you’ve finished answering questions, use the answers you like more. If you like both, edit and combine them—or make one a false rumor and the other the truth! Build on your players’ contributions, and twist them sometimes. Ditch anything you don’t like.
…The goal is to prepare whatever you need to comfortably run game, without railroading your game or preparing material of no use to you. This sweet spot can be elusive.”
Maybe this is different for you, but when I’m creating a world it helps a lot if there’s something that already exists so I don’t feel like I’m constructing it de novo.
Just as importantly, I need to feel like there’s something unfinished, somewhere ill-defined that I can dig into and fill with my own ideas. If fiction already exists to cover the space I want to explore and change, I have to overcome inertia and declare what changes I’m making in order to keep others onboard (this ties into Circles of Belief). That’s extra work that I could have avoided if I’d left open space.
Open space is an invitation. If I make sure to leave space around the edges of any given new detail, if I don’t fill all of the space with fiction, my collaborators can come forward with their own details and contribute to the whole. I think it’s just as true of linear fiction as it is with collaborative fiction.
This collaboration happens differently in various kinds of media. The reader of a novel imagines their own vision of the world, filling in little gaps that the writer left (intentionally or not). Viewers of horror movies will know what I mean when I say that the monster you don’t see, or only barely see, is far scarier than the monster you do see. That is its own form of contribution to the fiction—whatever nascent idea you had as a viewer came from you. You help scare yourself.
When it comes to roleplaying games, the collaborative fiction I mention above, that invitation is key to building the interplay of cooperative fiction making. A storyteller needn’t surrender all the details. You’re bringing your share to the table, after all. But leaving some of the details unsettled and open, or ill-defined and messy and waiting further clarification, gives room for other people to offer their ideas—which can be adopted in whatever form the gaming group sees fit.
That’s why, when I’m making settings for other people to play with, I always try to hit that sweet spot: not too much detail, not too little, with lots of space all around for other people to fill in as they like. If they don’t fill it in, I doodle a little more when I feel like it, and leave some room for later.