A great horror story needs a creepy atmosphere. This can be created by describing the setting in detail. For example, a dilapidated mansion with peeling wallpaper and broken windows. Another key element is a sense of dread. You can build this by foreshadowing bad things to come. Maybe a character finds a strange object that gives them a feeling of unease. And of course, a good horror story has a scary villain or force, like a shape - shifting monster or an ancient curse.
One key element is a strong opening. Hook the reader from the start with something scary like a sudden scream or a blood - splattered scene. Then, there's the element of isolation. Put your characters in a situation where they are alone and vulnerable, like being trapped in a cave. Tension is also important. Keep increasing it throughout the story by having the danger get closer and closer to the characters. And finally, end the story with a sense of lingering fear, so that the reader is left thinking about it long after they've finished reading.
The key elements are mystery and the unknown. Leave things unexplained for a while. For example, if there's a strange noise in the attic, don't reveal what it is right away. Characters are also crucial. They should be relatable so that the reader can put themselves in their shoes. And the climax of the story should be intense. It could be a final showdown between the protagonist and the source of horror. Also, use sensory details like the smell of decay or the touch of cold hands to enhance the horror.