Devise an original twist on an old theme. Readers of the supernatural will expect to see some of the conventions of the genre in your writing they've come to love over time, but they will also look for a new take on an old theme. This means giving them a story they won't expect. Get out a notebook and brainstorm a few ideas. Read some supernatural fiction or watch supernatural movies. Get familiar with what's been done, then figure out how to do it differently while maintaining the integrity of the genre's conventions.
Write descriptively about moods and setting. These two elements are extremely important in the supernatural fiction genre. The supernatural genre relies on evoking a sense of dread, a sense of trepidation and a large dose of suspense. Some supernatural fiction also relies on the "jump" factor, but even these moments in the story come after the previously mentioned elements have been in place. Don't simply write, "Barry saw a ghost." Build the scene. This is an example of how a first draft might go:
"Barry felt the hairs on his arms stand on end, as if an electric charge had passed by him. Something moved in the sliver of moonlight ahead. Thick fog hung just above the ground and moved in occasional swirls, so he couldn't be sure there was anything there ... except that he felt as if he were being watched."
Build up to the moment. Later, after all this description, Barry can actually see what it is he only previously felt.
Write in such a way that you highlight actions in your story. If someone is walking through a house, break your sentences up to pace the action. Here's an example:
"He opened the door. It creaked on its hinges as the darkness beyond was exposed. He heard something shuffle across the floor and thought about turning back, but he had come this far. He had to know what waited for him inside the house."
That paragraph could be broken up to better pace the action.
"He opened the door . . .
"The hinge creaked.
"The darkness of the room threatened to swallow him. He took a step and froze as something shuffled across the floor.
"He reconsidered going in, but he had come this far . . .
"Now he stepped into the darkness, ready to face whatever waited for him beyond the front door."
Keep readers in suspense for as much of your story as possible. Deliver the frights in increasingly larger doses. If you place your best work at the beginning of the story, you may place pressure on yourself to continually write bigger scares. If you follow larger scare factor elements with weaker ones, your readers will feel let down. Make each scare progressively more intense and keep readers on the edge of their seats.