What would make you put down a book without finishing it? What are some mistakes that writers should avoid? What storylines, plots, or tropes are you just tired of seeing?
Too much backstory is one for me. Backstory is not story, and I'm there to read the story.
I'd also add too many factual errors, like if characters keep getting bonked on the head, but come to just when the plot needs them to without any lasting harm done (I'm looking at you, Stranger Things 3). That's not how head injuries work.