Be aware of potential fiction vs. established fiction. Potential fiction is everything in your head that you haven’t put into play yet. It’s a “cloud” of possible things, organized according to the current situation. When the PCs infiltrate the manor house, you might have potential fiction elements in your head like this:
- Courtyard (wide open? filled with statuary?)
- Rooftop (loose tiles?)
- Underground Canal
- Sentries (professionals?)
- Guard Dogs (or other animals?)
- Electric Lights
- Fancy Locks
And then, when they say that they’re crossing the courtyard, you bring up a new cloud of potential in your head, by imagining that element in more detail, with its own features to establish, like deciding if the yard is open or filled with statuary.
As the players take action and face obstacles, you grab elements from the potential fiction cloud and establish them in the ongoing scene. Once established, they can be leveraged by the players. They’re a part of the game. Before that, they’re just notional—they don’t have a concrete “place” in the game yet. They can be freely incorporated as needed to address the results of rolls and to paint the picture of the ongoing operation as it hurtles toward its resolution.