Let's ask the master of horror on our forum.
Tagging
@Phyrebrat as he writes it well and recommends good books too.
V
Vaz you bum! I just saw this. You're cracking the whip innit bro (thanks for the compliment, though) .
To the OP:
(please imagine I've typed "IMO" in front of every sentence that follows in which I make a claim.)
Write horror. Read horror. Whatever that might be.
It has to begin with what terrifies you, not imagining some rarefied version of it for your potential readers, because we have to write what we know. If flying radiators scare you, then write about them. Personally, I don't get why people are scared of spiders, or why gore scares people (it bores me and it's lazy), but if I see those black scorpions with the huge claws that look more like boxing gloves, or tree crabs, or even small bats (esp where the wing meets the body), I freak out. These things are deeply personal.
You will hear the oft-vaunted 'You must have an opening hook' and you mustn't get that confused with a 'pow pow pow s**ts going down' opening.
I'd argue characters are far more important in horror than any other genre-genre; in SF & F you can have the cool worlds and the McGubbins which can distract or hide poor/simple characterisation (although, SFF authors often write wonderfully deep characters). In horror your readers have to care about the characters who will later be circling the plug hole. if you've not made your characters sympathetic or likeable, even, the reader won't root (and therefore not care) for them when their arm is ripped off, or they're possessed or whatever.
There's also a fundamental difference between SFF & horror which I see unappreciated when advice is given. You have to instill a sense of creeping, escalating dread. Therefore careful foreshadowing is far more important in horror.
Sci Fi is reflective of society and what is going on in society when it's written; horror is about the individual. Societies are made up of characters; the individual
is the character. Keep that in mind when writing horror, it's the thing I struggle with in mine the most.
Finally, here's a how-to book:
Sorry for being late to the party.
pH