I'm just going to jot down some thoughts coming out of a discussion over lunch with my son about Stephen King and horror fiction and stuff. Other thoughts or speculations?
1) Horror is not just a genre. Like "romance" and "mystery" and "suspense," it's an emotion that can be generated within a book about something else. Why would we want to have a scene or passage or more of horror in a non-horror-genre book? To deepen the darkness of the book? To heighten the relief of a happy ending? I do think that horror would provide contrast (in the color sense) to the rest of the book, as long as it doesn't overwhelm with darkness.
2) Horror is not about the dreadful event... it's about the dread of the event. As with suspense, the buildup becomes all-important, to create that sense of dread within the character and the reader. Scene design, word choice, pacing-- these must combine. Pacing will slow down, sentences will lengthen, so the scene can lovingly, almost lubriciously, develop the creepy horror-ness. Presentation (the development) will be more important than plot (the event).
3) Horror is created by -knowing-. You have to know what's coming to be horrified by it. (Looking back on a horrible event works too, because you -know- it can happen now.) Notice how in "The Lottery" Shirley Jackson builds the dread by making it clear that everyone in the village knows what's going to happen (even if the reader doesn't). Go ahead, read the story (it's only eight pages), and see how the relatively bright tone in opening paragraph becomes progressively darker as the festive mood gives way to anxiety. The villagers all know what's coming.
4) Horror is inspired by the writer taking access to his/her deepest fears. But the event doesn't have to be all that dramatic. What's important is that either it's a common fear, or the writer describes the feeling well to make the reader "know" it.
Stephen King, I remember, was asked what in his life prepared him to write horror, and he spoke of two very common, nearly universal events. Once, when he was a child, he had an ear infection, and (presumably this was before antibiotics were used routinely) the doctor was going to lance the eardrum to release the pus. The boy (King) knew what was going to happen and that it was going to be terrible, and ran and hid in a closet. And his mother and the doctor had to come and drag him out and perform the procedure. Maybe few of us get our eardrums lanced, but we all got shots (I have to inject myself with medicine, and no matter how often I have done it, every single time there's a moment of horror involved in the breaking of the skin).
(I'm writing from memory here, so tell me if I have the details wrong.)
Then the other incident was watching one of his children run into danger (collision with a snow plow? I forget) while King was too far away to rescue the child, and had to watch in dread (there's that word again). (Nothing happened, but every parent has memories like this.)
Just take it slow. Read King's horror scenes, or Dean Koontz's, and see how slooooow the scenes develop. You can't shorthand horror. Dread has to build, through gradually darkening events and prose. That takes time and probably several revisions. It's not adventure. It's slow-paced, not fast-paced. There really aren't any shortcuts to horrifying readers.
5) To get in touch with what will horrify, remember your nightmares, and study the most common nightmare types. If you can invent scenes that include some common nightmare element, you'll be making a direct connection to our subconscious, and to the collective unconscious.
For example, one of my recurrent nightmares is seeing a plane on fire in the night sky, and it sails over a ridge, and then I hear an explosion and see a fireburst on the ridge. I suspect most people have a nightmare where (as with King's example above) they know something terrible is about to happen and can't stop it. That would make a great horror scene (especially if at that moment, the character had a friend or loved one taking a flight).
Another recurrent nightmare I have-- and you probably do too-- is being chased. But with mine, there's an added terror. I run through a shadowy street to get to my own front door. I fall into my house, slam the door closed, stand there panting but relieved. And then, slowly, I become aware that whatever was chasing me is in the house. And I'm locked in with this evil.
Now if that sounds familiar, it's probably because you've seen it in a few horror movies.
6) Horror elements, as a conduit to the subconscious, can trigger strong emotion even in other types of scenes. An example is the famous burlesque scene "Slowly I Turn," which uses the slow, mechanical, and repetitive language of a horror film to comic effect.
(Here's Lucille Ball: Slowly I Turn, Step by Step.)
That horror scene of the chase through a shadowy street? Watch the end of Gone with the Wind. It's a romantic "horror"-- the terror that is "chasing" her is her fear of abandonment, and she gets home, and there is Rhett, and she sighs in relief-- she's home. She's safe. But then the terror is right there with her, in her own home: Rhett announces he's leaving.
If you want strong emotion, whether it's comedy or romance, try using the horror tropes in some way.
7) Horror is, at essence, about a fear of loss. Just as Scarlett feared losing love, a horror story character might fear losing control, or losing face, or losing trust, or losing some power. You know what's a great horror story? Flowers for Algernon. In that story, researchers manage to increase the IQ of a white rat (Algernon), and then try the technique on a man of low IQ (Charlie). Rapidly, he becomes a genius, and for the first time feels the great pleasure of learning and inventing and understanding. (And he falls in love.) But then Algernon begins to fade and lose his genius at running mazes. Charlie, witnessing this, realizes that he too will shortly be losing all the intellectual gains he made. This is the horror. He knows what is coming. He dreads the loss. He can't stop it.
That is how we create horror. Establish something of value, and then predict its loss.
What else? What do you think? Help?