A good horror story opening usually has a creepy setting or atmosphere to draw you in right away. Maybe it's an abandoned house on a stormy night or a dark forest with strange noises.
You could introduce a mysterious character or an unexplained event. Make the reader curious and on edge from the get-go. Also, use vivid and spooky descriptions to set the mood.
The old house stood at the end of the lane, its broken windows like empty eye sockets staring into the void. This opening line creates an image of a desolate and potentially haunted place, drawing the reader in.
The opening paragraph sets the scene, say it's about a dark forest where strange noises are heard. I'd continue the story like this. I entered the forest, my flashlight barely cutting through the thick darkness. Every step I took seemed to echo, as if something was following me. Then, I saw a pair of glowing eyes in the distance. I froze, not knowing whether to run or stay still. The eyes started to move closer, and I could hear heavy breathing. I finally mustered the courage to run. Branches whipped at my face as I sprinted through the forest. I tripped over a root and fell. As I looked up, a large, shadowy figure loomed over me. It reached out with long, claw - like hands.