Minimum Detail
Overview first, zoom and filter, details on demand. - Ben Shneiderman's information-seeking mantra.
In an apparent paradox, I find both the node-based scenario and the Carved from Brindlewood approaches to prep unsatisfactory. The first is too rigid; the second is too loose. I want there to be a core truth in the GM's mind that informs how the world responds to the players. I want there to be a reasonable cause-and-effect to everything that happens. Cause and effect is hard when you don't control both sides of that equation, and I think that's part of why working in this medium is so difficult!
So, why did I prep a dungeon map and a Meatgrinder for my His Majesty the Worm game? Because in a dungeon game, that level of concreteness is the minimum prep. I find working on a dungeon like that to be fun and fulfilling, because I know it will be useful.
On the other hand, for Homefront play yesterday in Stonetop, I did no prep whatsoever. I think one of the reasons Stonetop is so good is that the Almanac provides detail on demand, but also a coherent overview of the setting. You can go a long way in that game without explicitly prepping because Jeremy did so much work for you! The setting is so rich that I instinctively have lots to draw on, but if I want a detail in a moment, I can find it quickly.
When running Triangle Agency, I need to know the core truth and invite the players to explore that truth however they see fit. If you know the core truths of the Anomaly, then all of its impacts should1 fall into place. I want someone who reads a Triangle U Mission to be able to internalize the Mission and only consult the book when they need a quick reference.
To me, prep means writing enough detail, but not too much. But enough is probably less than you think. Thus yesterday's piece on abandoning prep. The Liminal Horror style guide uses extreme terseness to accomplish this. Under Hollow Hills's Occasions are lightly held. Some publishers are renowned for having verbose, novelistic keying styles, though, and people like that too. Character Studies points at some different approaches to NPC writing, but what they all have in common is clearly communicating character. What do terse and verbose keys have in common? They give the GM enough to confidently be present.
Ultimately, presence remains the key. If you have enough information that you can look away from the page and be present with your players, that is enough prep. And that amount is very minimal indeed.
Emphasis on "should." I think part of why writing good Triangle Agency missions is so hard is deciding core truths that are clear enough that this statement becomes true! It's definitely something I'm working on in Triangle U.↩