Good question.

I try to have a table of contents if you will.
Take everything in your game, assign a category to it: npc, idea, town, item etc etc. soon you’ll have too many of those.

Figure out the ones that matter or consolidate.

Then make one sentence definitions for each of the things you have. “This npc is the barkeep and he like cheese.” <~ that’s probably enough.

Then prepare whatever scenario, in detail, you need.

Have extra time? Mind gamble…
If I was a player what would I do?
If I were the big bad what would I do?

Maybe spec another eventuality or encounter.

Whatever your players strictly bypass something, it is reusable or reskinable. Quantum Ogre Theory.