Some observations about horror tropes, after reading too many haunted house novels and watching the same characters walk into basements they shouldn't.
The haunted house story lives or dies on whether the house has agency. Shirley Jackson understood this. Hill House doesn't just sit there waiting for someone to find a scary room. It rearranges itself. It chooses who to work on. Most haunted house novels treat the building like a stage set, a place where scary things happen to occur. Jackson treated it like a character with preferences.
Writers use the "don't split up" trope because isolation is the fastest way to remove a character's safety net. I get it. But every time I read a scene where four people decide to search a dark building in four different directions, I can feel the author's hand on the wheel, and it pulls me out. The better version is when the group gets separated against their will. That's scarier anyway, because now the environment is doing the work.
I think the scariest sentence structure in horror is the short declarative that follows a long, winding description of atmosphere. You spend three paragraphs on the quality of light in a room, the dust on the windowsill, the particular silence of a house at 3 a.m., and then: "Someone was sitting in the chair." Jump scares don't translate to prose. But the sudden intrusion of a fact into a mood translates perfectly.
The ancient evil that awakens after a thousand years almost never works. The problem is motive. A creature that's been sleeping since the Crusades wakes up and, what, wants to eat a suburb? The best horror villains have comprehensible desires, even if those desires are monstrous. You can't build suspense around something that has no logic the reader can track.
Stephen King wrote in Danse Macabre that horror fiction is "an invitation to indulge in deviant, antisocial behavior by proxy, to commit gratuitous acts of violence, to discover our most unspeakable desires." I think the more interesting version of his argument is simpler: horror lets you rehearse the things you're afraid of in safe conditions. You practice being terrified. You practice surviving it.
The final girl trope gets talked about like it's a formula, but in its best versions it's actually about competence under pressure. The one who survives pays attention.
Horror and comedy work together because tonal contrast sharpens both edges. An American Werewolf in London is funnier because it's genuinely frightening, and it's more frightening because you were just laughing. Get Out does the same thing with social comedy. The moments where you're smiling at the awkwardness make the moments where you're not smiling so much worse.
Familiar settings are almost always scarier than remote ones. A cabin in the woods is scary in theory, but a suburban kitchen where something is slightly wrong, where the light is a little too yellow and there's a smell you can't place, that stays with you longer. The contrast between normal and wrong is what creates dread, and you need the normal to be truly normal for the wrong to register.