Offer some guideline options for Narrators to include in their story descriptions to help players understand the expectations of what they should and shouldn't do to other characters and how to interact when making moves. Examples:

"use the comments box to let other people know you are typing a move, and when you are done with it"

"use 3rd person omniscient point of view"
"use 3rd person subjective point of view"
(along with example/definition)

"please do not write actions for NPCs or other player characters"

"feel free to write actions for NPCs if you have control of the story, but still don't write actions for other player characters"

"feel free to write for all characters in the scene when you have control of the story"

"feel free to ask for plot clarifications when you have control of the story so we can move in the same direction"

"feel free to go any direction you like when you have control of the story - as the narrator I'll catch up"

As I started my first two stories as a player, these are all questions that I ran into, and some of the other players seemed to struggle with as well.