To make a horror story, think about people's common fears. Isolation can be a great element. Imagine a person stranded on a deserted island at night. Add some supernatural elements, such as a ghostly voice that calls their name from the ocean. Use vivid descriptions of the environment to create an eerie atmosphere. The cold wind blowing through the palm trees, the sound of waves crashing in an almost menacing way. And don't forget to create a sense of dread throughout the story. Let the character feel like they're being watched even when there's no one around.