As A Rogue Spirit said, it would be great if as part of the game setup (or possibly as part of Character creation) were some options to help guide the game and be sure all players are operating with a common set of assumptions.
In a game I'm playing currently, we've been discussing what the boundaries are in relation to another Player's Character when writing a Move - whether or not it's ok to write dialogue for or give actions to another Player's Character.

It's going to be different from game to game; narrator to narrator; and character to character. Some people may feel a strong sense of 'ownership' as regards their characters and want other players only to react to their characters - not actually 'pull the strings.'

Other people may be perfectly fine with someone else using their character - especially if it moves the story along better - and may actually be excited by an idea another player introduced for the character.

If this was an option or toggle during game set-up (or during character creation), then there's less chance of accidentally stepping on someone's toes by using that person's character in a move you are making.

Also it would be great to have set in stone the idea that you *build* on what's come before you, you don't *negate* it. Had a couple of games with sneaky characters doing something stealthy only for someone (usually inexperienced RPers) to immediately pull the AHA and reveal them/stymie their move. It's dull and stifles everyone who tries to do something different.

A tab for "House Rules" could be one way to fix this - as a separate drop-down box entity under the game description, it wouldn't clutter up the scenario description for when you're scrolling through new games etc.

Yes, please for the love of God at least put in the creation of a game some settings for the Narrator to say if modding other people's character's is allowed or not. I'm so used to sites where powerplay and god-modding is illegal that it is frustrating for me when someone picks up control of my PC without talking to me first. I don't mind people doing that if I know it is going to happen but mostly I'd like to create a game where I can point out that the challenge of turn based writing is manipulating the situation to your advantage not making another person's character do or say something you have no idea if they would actually say or do. Maybe a function so if the person wants to do that they can tag the player into the post for the player's approval?

I agree, but not just to keep power trippers in check. Newbs like me would benefit from a list of short guidelines for players such as don't take control of other players when making your own move. A list for narrators as well, lessons learnt from narrators who have run a few games. Guidelines only, because you wouldn't want to stifle creativity.