What not to do

Don't plan a storyline or a plot. Don't plan the PCs' character arcs. Don't plan dramatic moments, where the PCs arrive just as this particular thing happens (regardless of how long they took to get there or what they did before). Don't assume the PCs will take a certain course of action, or that they'll succeed or fail at a particular task. All of that flies in the face of playing to find out what happens. That's you deciding what will happen, in advance, by yourself. Absolutely not what you're here to do.

Instead: prep situations, and possible encounters, and places to explore. Prep threats and NPCs with good actionable instincts, maybe some grim portents and impending dooms. See the Prep section Prep for how to do this.

Don't tell them what to roll before they've told you what they're doing. You do not get to say crap like "the bandit attacks, Defy Danger with DEX." Because 1) That's not how it works and 2) What if they don't act quickly or with finesse (the trigger for Defying Danger with DEX)? What if they knock his attack aside and bash him with their shield? What if they take the blow and run him through? What if they toss dirt in his eyes and kick his groin? When you tell the players to make a move, without them first telling you that they've done something to trigger the move, you're taking control of their characters and dictating what they do. You're breaking the rules of the game.

Instead: make your soft GM move and ask, "What do you do?" Then, based on the answer, decide together whether they triggered a move and which move they triggered. Then they roll that move, and you resolve it from there.

Don't make them roll "just because," or because "maybe they wouldn't notice," or any of that garbage. Like, you know how in other games, you'll decide that a monster is sneaking up on camp and ask the PC for a perception check? That's not a thing in Stonetop.

Instead, you just make a soft GM move, like announce trouble, that hints at the monster's presence. "You realize that the crickets have all gone quiet. And then, maybe it's just your imagination. But you thought you heard something… laughing? Out in the woods. What do you do?" And maybe they wake the others or maybe they call out or maybe they peer carefully out into the woods and cock their head, triggering Seek Insight. However they respond, you run the game from there.

Don't stop making GM moves, especially when the players roll 10+. You'll describe what happens, yeah, and you'll give them the success that they earned. Sometimes a player will just grab the initiative and follow up (and that's cool, run with it). But usually, the players will still be looking at you to see what happens. The fiction churns along and bad guys keep doing bad things.

So when the Heavy rolls a 10+ to Clash and deals her damage and the foe's still standing and there are like two other baddies nearby, don't just go, "Cool, he's still standing, what do you do?"

Instead: think about how the first foe responds to getting hit, and what the other two foes are doing. Make a move that takes all that into account, and then ask "What do you do?"