I did not expect to get to Dreamation this year, but My wonderful wife surprised me with a window of time that allowed me to day-trip up for the last day of the convention. Didn't play anything, and didn't get to see everyone, but still very much enjoyed myself.
Part of my fun was sitting down to talk with Brennan Taylor. Nominally, it was for a podcast, and he's got 10 minutes of me talking about hacking games that will no doubt be unleashed on an unsuspecting world at some point down the line, but after that, we got to talking about setting. This was a little bit catalyzed by talking about his forthcoming game, Bulldogs, which I'm pretty excited for, but it was also kind of general. From this conversation came three points that I'd like to share with anyone looking to write setting material, mostly out of a selfish desire to make it all interesting to read.
First: Write Around The Holes
As a tribe, we're smart people who like to show off how smart we are, and that lends itself to a completust streak. We also like our books, and we have an instinctive understanding that world building is something which should usually yield to the necessities of story. These elements combine to create complete, cohesive settings with satisfying narrative arcs and it's terrible.
If you're writing a setting for play, you are not telling a story - you are creating an opportunity for someone else. This doesn't mean that nothing should be going on - quite the contrary, things should be hopping - but they should not be resolved. It is ok to set things up and then just stop. Our instincts may want to resist, but by doing so we create the opportunity for people to fill those holes with play, which seems rather the point.
Settings that fail to do this may be interesting and colorful, and they may be entirely satisfying as a pure backdrop of play (that is to say, interchangeable dungeon storage) but if you want the setting to matter, leave the holes in place and trust someone else to fill them.
Second: Playable Is Better Than Clever
In jokes, word play and other setting elements that have nothing to do with play and everything with the author squeezing in something cunning need to be used with the utmost caution. This is not to say text needs to be all serious - jokes which include the reader or the occasional easter egg can be fine, but if you're just showing off, knock it off.
Short point, I know, but there it is.
Third: The Three Sentence Rules
Virtually any setting element can be fruitfully described in three sentences: a description, a distinction and a hook (they don't literally need to be three sentences, but you get the idea). For example: Varn Kasi is an Ethari crime lord (description) based out of a gentlemen's club overseeing the Alverado harbor (distinction). He's making preparations for war against the Dwarf gangs horning in on his silver dust trade (hook).
That is not a lot of information, but it's enough to play with. A GM can absorb that from a book and very quickly plug it into actual play. You really don't want to use less information than those three sentences - doing so can cause the reader to wonder why you're bothering to mention it at all. But on the other hand, you want to have a very good reason to provide any more information than that. Obviously, you will want to do so for the central elements of your setting, but it is worth challenging yourself to determine what more you really need to add. See, the three sentences is a sweet spot. Every additional piece of information you add takes longer to absorb and - almost paradoxically - often puts more limits on the element in question.
This need not be so. If the extra information is kept sharp and focused on how it will come out at the table, it will probably work out. And the best way to make that happen is to really ask yourself how you're improving on those three sentence.
So, three guidelines. They're not hard and fast rules, and they are probably a bad match when you are talking about worldbuilding in fiction, but gaming has different priorities, and it's important to remember that a game's setting should not be a reformatted novel. If you want to write a novel, then write a novel. Heck, it might even make for a great setting to game in once your done. But if you're writing setting, then write for play.