A couple of models you might find useful:
We’ve used the Rocket model for this with Leadership teams which is pretty good at breaking down key areas that feed into the shared goals. It’s regularly reviewed to ensure they’re living up to their commitments / ways of working
I’ve also used 5 dysfunctions of a team model for creating a mandate / charter for cross functional teams. We agreed key principles / behaviours we would want to see at each level and again review progress against but this time with cross functional peer to peer feedback.