Check out 25 Things You Should Know About Writing Horror by Chuck Wendig. My produced Invocation short scripts are horror, and most of my earlier feature specs are horror-tinged — starting out as horror, and migrating in rewrite to more action-adventure with ghosts or what-have-you. I’m also contemplating a contained horror script as my next project, since most of my other feature specs are fairly big-budget.
7. Dread and Revulsion in an Endless Tango
Beneath plot and beneath story is a greasy, grimy subtextual layer of pacing — the tension and recoil of dread and revulsion. Dread is a kind of septic fear, a grim certainty that bad things are coming. Revulsion occurs when we see how these bad things unfold. We know that the monster is coming, and at some point we must see the wretchedness of the beast laid bare. Dread, revulsion, dread, revulsion.