Or really, ask?
How about this: the players are engaged in improv, with the general topic as the premise of your game. You’re kind of observing, sitting back and throwing a wrench in the works every time they get too comfortable, and nudging them back into the theme every time they drift too far. What do you ask, what do you suggest, what do you say to make that happen?
The first draft of this post was a lot of inside baseball, and so to counteract that, I’m gonna try to go heavy on the examples.
Let’s look at Fiasco: Jason says “hey, this is a story about things going wrong. Every scene, I’m gonna ask you whether it goes generally well or generally poorly for you, and you can answer, but remember: if things go too well too often, you’ll run out of good luck and things will go ill, so you might want to take some punches.” He’s asking two of the big categories of question: “how’s that turn out for you?” and “what’s that outcome cost you?” He only gently nudges you back to the feel of the game in part because the feel is pluggable—different playsets will produce different initial elements, and it’s up to you to remember to bring them in.
Let’s look at Apocalypse World: Vincent says “There’s no status quo in Apocalypse World, but you’re all cool and competent and sexy, so you can probably navigate it.” Every time a move triggers (roughly every beat, or more accurately, every beat that catches Vincent’s attention as particularly interesting), he asks you “Hey, hold on a moment. Are you sure? There might be a cost, or some interesting side effects,” and you often roll dice to answer the “are you sure” and to frame the “what cost?”
So, oh hey, maybe we should pause to note that there’s a common element here. If you’re at the table, you can interject when something catches your interest. When you’re operating through rules, you need to tell the players when to bring them to bear (though, of course, this can and ofteh should involve some degree of judgment). Jason says “every scene, at about the tipping point of it”. Vincent says “on these beats that I like”.
Let’s also circle around again for a moment to the “what does it cost you”: fictional costs are great, of course, but if certain costs are recurring and structured, you might want to make some mechanics around them. Stress tracks, limited pool of scene dice, spending Hold in Powered by the Apocalypse games, these are all costs. Even “you get one action on your turn, what do you spend it on?” in very turn-ish games.
To operationalize this: maybe run your game as loosely structured freeform, and pave the cowpaths. Every time you pause the game to ask a question or suggest an outcome or shape the fiction, consider making a rule around that. In Arcadia right now, there are a few things that I often want to know: “do they take your meaning or misunderstand?”, “are they offended by your actions or words?”, “who else overhears or mishears?”, “how do you really feel?”. There are costs I see recurring: emotional tolls, relationship tolls, reputation tolls, moral tolls, opportunity tolls. One thing I need to answer for myself: how do I know to ask these questions or put forth these costs beyond “it feels right?”.
I’d be interested to see more examples of this “rules as designer-asking-questions” in other games; right now, I can see it at work in plenty of Vincent’s games, but I want to avoid myopia, so let me know where you see this at work.