Follow the rules

There are many rules, especially in the form of player moves: basic moves and follower moves, special moves, exploration moves, and steading moves. Each playbook has moves. Inserts have moves. Arcana have moves. Dangers, discoveries, threats, and locations can all have player-facing moves.

Hopefully this is obvious, but: when a move is triggered, follow the procedures in the move and say what the move requires of you. The rules are there to push the conversation and the fiction in certain directions, and to clarify what happens in moments of uncertainty.

Give the players the full benefits of their moves and their rolls. Challenge their ability to trigger those moves, sure, and temper the results based on the established fiction and your prep. But don't fudge the results of a move because you think things should go a particular way, or because you're worried that things will be "too easy" or "too hard." That's not your job. You're playing to find out what happens, right?

You don't get to invoke a player move unless its trigger is actually met. You don't get to say, "The crinwin attacks you, roll +DEX to Defy Danger!" Gods, no. You say that the crinwin leaps at them and ask, "What do you do?" If they do something that triggers a move, then you do that.

It's okay if, in service of your other principles, you suggest something in the spirit of the rules instead of following their exact letter, but be up front about it and get consent. "You got a 7-9 to Clash? Roll your damage. 9!? Yikes. So, I know it says you expose yourself to your enemy's attack but I'm thinking the 'attack' in this case is that your axe gets wedged into his skull and it's gonna take a bit to get it free. That okay with you?"