As writers, the middle of a fiction project - whether it's a short story or novel - is often our undoing.
Some writers bog down and trail off and wind up putting an unfinished manuscript in a file. Some plod through and work to fix the problems on subsequent drafts.
As readers, sometimes we put the book down and don't pick it up again, or we stop reading and go to the next story.
The middle of a story - long or short - is no place to take the middle road.
One way to avoid a muddled middle is to tap into characters and tie them tightly into plot. Plotwise, we're told to pile on the trouble. With each chapter, ask ourselves what else can go wrong. What more dirty deeds we can go wrong for our protagonist.
While you're asking these questions, don't forget about your character. If he has an unrational fear of snakes - think Indiana Jones - play that up. If she's afraid of her shadow, it's the time for her to become more paranoid about everything happening to her. Because of her fear and paranoia, she searches for ways to defend herself. And in doing so, causes more problems.
So heap on problems that fit your character so that plot and character become entwined.
It's one sure way to unmuddle your middle.