Hit a short, sharp piece of music or a sound effect at the exact moment the frightening thing appears. The sound makes the shock much bigger.
Jump scares, the moment a monster or killer enters the frame, and twist cuts in short-form.
Generated sound differs in volume and texture from clip to clip, so it is hard to use as a sting. Make or pick the sting yourself (a string scrape, a metal hit, a low "thud"). Line up the start of the sting with the first frame where the subject appears (adelay, amix). Lowering the background music just before the sting makes it hit harder. Don't repeat the same sting in one video.
Two-shot sequence: Shot 1, a quiet attic with a dusty covered mirror and a dim lamp, near silence, 4 seconds; hard cut to Shot 2, the cover slides off to reveal a cracked mirror with a shadow behind it, with a single violent string stab (the sound sting) hitting exactly on the first frame, then a low rumble fading out, 3 seconds.
Halloween (1978) — John Carpenter said he tried to land the sting at the exact moment something enters the frame, and when his hands couldn't keep up, he lined it up in editing (Hollywood Reporter) · Psycho (1960) — In the shower scene, sharp strings screech along with the knife strokes (Hollywood Reporter)
AI With TechZnap — Sound design for horror scenes with AI (Makes horror-scene sound with AI music and sound effects. Not verified whether it covers stings on their own)