My drama teacher for five years was the amazing Nancy Drake. One of the lessons she drilled into us was this: "Acting is a specific reaction to a particular set of circumstances in which you believe utterly."

Break that down:
"A specific reaction" – general, vague reactions like “I’m annoyed” are out. No small emotions. Show us only specific recognizable and strong reactions to what your character sees and knows.

"to a particular set of circumstances" – It is this moment in time that you care about.

"in which you believe utterly." – If you don’t believe, then why should the audience?

The application of this type of theatre principle to writing a novel is obvious. Writing must be specific.

Each character must react to the particular circumstances.

Each character must be able to believe in a) what is happening, and b) the actions they are taking in response.

If you ever catch yourself writing “Tom knew he shouldn’t be doing this, but...”

Think again. The circumstances, his needs, must COMPEL Tom to do what he is doing.