Add minor, common sense details freely. Make assumptions and add set dressing to scenes to play off of to keep things flowing dynamically. There’s no need to check in with the GM - they’ll step in if a detail goes beyond set dressing. Anything that’s a given for your vantage, like knowing someone or having equipment that makes sense, is set dressing.
Character-driven complications you introduce into a scene and have to follow-up on. In return, you take spark. Tangles must stem from your vantage or story arcs nad always have an immediate impact, like an action roll, an option closing off, or forcing inaction at an important moment. These are things like:
Pure cinematic momentum. Each session you have 2 story. Spend it to add story details that go beyond set dressing, creating new opportunities or shifting the scene in your favor. Added details must fit your vantage, at least as a stretch, or tie to a story arc. Example details:
Added details can’t override rolls or contradict the established story. If your detail affects another PC, get permission. The GM can make a story roll to see how true or beneficial it is, or add nuance. On a grim, it may backfire! The GM can also veto details to keep things coherent.
There are gray zones between set dressing, story details, and details simply too impactful to add. Set boundaries with your group.