Run through the adventure in your mind
Ever since I started doing this deliberately, as one of the steps I take when preparing for the game, I feel much more confident in my ability to run a good adventure.
If you haven't done this before - you really should try it. Here's how it works:
- Picture yourself running the adventure. Imagine sitting at the table and GMing the story for your players, describing the scenes.
- Visually imagine the scenes, try to vividly picture what's going on, try to see the whole story as a movie in your head.
- Imagine the adventure from the players' perspective, imagine playing through it as your own character.
Notice all the gaps:
- The moments when you can't picture what the scene looks like.
- The moments when you don't know what happens next.
- The moments when you'd ask some obvious question or take some obvious action as a player, but don't know how to respond to it as a GM.
Add the biggest, most noticeable gaps to the list of open questions. Don't try to account for every small detail - just focus on the things you would find the most difficult to improvise during the game.
Then go through the list and figure out the answers to these questions. Once you're done - you'll feel much more confident that you know the story and can handle whatever the unpredictable players throw at you.