Tap into your greatest fears. Remember events that have frightened you or try to imagine the worst possible scenarios that can occur in your life. Remain in touch with your feelings about these frightening ideas so that you can convey the sense of horror.
Read horror. If you pay attention to how the writer creates feelings of suspense and terror, you may gain ideas as to how you can create these effects yourself. Also, if you read horror stories, you will gain a sense of what has been done already and then you can try to create horror stories that are more fresh. Readers become desensitized to overused writing cliches and will not be frightened by your story.
Come up with a series of frightening events and then arrange the events in order from least frightening to most frightening. This will maintain the suspense the longest.
Create a protagonist that the reader can identify with. If you want to create an unusual protagonist, still try to give him some emotions or other traits that the reader can find in herself. Making the characters strong will cause the reader to realize that horrible things can happen to even strong characters.
Decide where you want your setting to be. Choosing a setting that readers will have familiarity with will help them identify with the characters more. However, it is always helpful to throw some bizarre elements into the setting like a pet cemetery that resurrects dead pets.
Sprinkle in gore, but do not overdo it. Excessive gore pushes the readers away from emotions of fear and toward emotions of disgust.
Reveal information slowly to the reader. Giving information away too quickly makes the story too predictable, but taking too long causes the reader to become bored and give up.
Introduce all of the characters early on in the story and then focus almost entirely on the plot.
Have the surviving characters triumph in an original way that shows character growth.