I watch a lot of horror, and the one trope I'd get rid of immediately is cheap jump scares. I'm talking about the ones that are completely inorganic and have no real place in the story or even the scene except that someone said, "Let's do this and make the audience jump."
The most recent example I can think of is the final frame of the film Sinister, which is a great horror film, in my opinion, but the end cheapens the entire experience. We've had this tense, suspenseful film with a twist ending that's earned, but just before credits roll, the villain's face pops in from the side with a loud noise to stare into the camera for a second. It's stupid, pointless, and lessens the film by its cheapness.
My go-to violator, though, is Friday the 13th Part VII: The New Blood. There's a post-coitus scene where the guy has gone downstairs to get a beer, and the girl is left in the room by herself. She hears weird noises and gets freaked out, looking around for the source. Then all of a sudden a cat jumps into the frame with a loud musical sting. We've never seen this cat before. We will never see this cat again. It's the first and only time we have even the slightest inkling that there's a cat that lives in this house. It's ridiculous.