This is a simple thing, but too often writers forget. In a story everything means something.
The character you are focusing on when an event happens needs to react to what ever just happened. If the event didn't inspire a reaction it doesn't need to be in the story. I realize that almost sounds like a rule and it probably is but its a very flexible rule.
In MIND THIEF, I had a problem character. This girl Debbie was just there until the her major scene. The problem wasn't her, it was my main character's reactions to her. He didn't have any. She humiliated in public then apologized his first draft reaction, “That's nice”. Final draft reaction, “Well that takes some guts”.
Later when she slips out of her accent he laughs at his paranoid thoughts that her losing her accent makes her evil. (it does).
The reactions don't have to be huge but they have to be there.
In an pure action story the reactions are simple. Something happens and the character can attack it or use it for an attack later.
One scene I am always remembering is in the original (worth watching) Wayne's World. The driver for Mr. Big's Limo pulls Wayne and Garth aside and explains the communication rig set up in the limo. Wayne asks why he is showing it to them, the driver says, “You might be interested in it later.” Later they use that information and Wayne says, “Gee, at the time I thought it was just extraneous information.”
If it's not a comedy you should probably make it a bit more subtle, but the same rule applies. Wayne didn't just absorb the “extraneous information” he wondered why it was being given to him.
If the character doesn't react to what you've put in front of them the reader won't react either. If the reader isn't reacting long enough, they will react by putting the book down.
The reactions don't have to be conclusive, most of the time it's better if they aren't. Wondering why is a normal reaction. Jumping to the wrong conclusion is a reaction. But the character has to react.
By Darrell B. Nelson author of I KILLED THE MAN THAT WASN'T THERE