1. Characters can lie to the reader.
Blink and you'll miss it, but there's a very chilling line in Stanley Kubrick's The Shining that's set up early on. At the start of the movie, Wendy Torrance talks to a doctor about her husband Jack's drinking. She tells him that Jack broke his son Danny's arm once, but that it was an accident that happened when he was drunk, and that Jack hasn't touched a drop in six months.
Then, halfway through the movie, a half-crazed Jack is talking to a hallucinatory bartender, complaining that Wendy will never forgive him for what he did to Danny. He was just drunk, he says, and besides it was three years ago!
|F@#$ you, Dad.|
2. Remember the small details.
Personal moment: one of the biggest problems I have is that I write "thin", which means that I tend to focus on plot and dialogue at the expense of extraneous details.
Stephen King doesn't have this problem. Hell, he claims to have exactly the opposite problem, and forces himself to cut at least 10% from his books during editing. (Hefting Under the Dome, I think he might have relaxed this policy.) And while he was a filmmaker, Stanley Kubrick was very focused on getting every detail right: just look up the stories about the endless reshoots he put Shelley Duvall through.
So what are the benefits here? Well, just look at Room 237. Someone put together an entire movie of nine people using details from Kubrick's version of The Shining to explain that the movie was really about Nazis, or Native American genocide, or whatever, and it's all believable. Or consider the fact that Kubrick deliberately laid out the Overlook's rooms in a way that's physically impossible, just to make the hotel that much creepier for the viewer's subconscious. Or - why not? - go read the Dark Tower series, where Stephen King pulls maybe a hundred different dangling details from his other books and uses them to create a setting that's absolutely insane.
Small details, well chosen, will stick in your reader's mind and give rise to new ideas. It'll make for a richer experience for your audience. Or, you might be able to use the little details yourself to build a new story.
3. Use the reader's imagination against him.
This follows on from the above point and sort of flips it on his head. In the novel The Shining, Stephen King includes a scene where Danny Torrance is playing in a sort of playground tunnel at the Overlook. All of a sudden he starts to imagine another kid playing in the tunnel, a dead kid. And he can hear the sound of the kid behind him, scratching as he claws through the tunnel, wanting Danny to save him, or at least stay and play with him, forever...
You've got a picture of some horrific abomination crawling after poor little Danny right now, right? Well the thing is, King never describes what the dead kid looks like. I'm pretty sure Danny never sees him, and for all we know it could have been his imagination. (Hint: At the Overlook, it's never your imagination.) But your scared little rat-brain has taken a few sounds and Danny's imagination and conjured up a version of his horror that's your very own.
A few choice details can prime your reader to imagine a whole host of things you're only hinting at. And because those things come from the reader, they're going to be a lot more personal and a lot more powerful. Sometimes telling a story is about getting your text out of the reader's way.
4. Villains have good points, heroes have failings.
In Stephen King's The Shining no one is a completely irredeemable asshole. Nor is anyone a saint. Just to take a few examples: Jack Torrance turns into an alcoholic rage monster, but he loves his son deeply and wants to do right by his family. Wendy Torrance is a good mother and becomes a strong woman, but she's badly afraid of following her own mother's hateful example and defers to Jack when she really shouldn't. Danny's a very bright kid, but he's still a kid and he tries to ignore his very real concerns with the Overlook until it's too late. Dick Hallorann is an example of the Magical Negro, but he causes a great deal of damage by failing to warn the Torrances off and his charge to the rescue turns into a complete clusterfuck.
I suspect that one of the things that really irritated Stephen King about Stanley Kubrick's version of The Shining is that he didn't keep this point in mind, or else he didn't worry about it. Jack Torrance is basically a lunatic from the get-go, he's just pretending otherwise when the movie starts. Wendy is practically the poster child for spousal abuse, and never demonstrates the inner strength King credited her with. Danny is more of a plot device than a character. (To be fair, Hallorann is pretty faithful to the original.)
Now, Kubrick's version of the characters still works very well, but part of that is because the cinematography makes up for it, and part of that is because Jack Nicholson is just such a delightful lunatic. Without the Overlook and without Nicholson, I don't think they would have been able to support a movie. King's characters, on the other hand, have enough complexities and faults that they'd be interesting to read about even if they weren't living in a haunted hotel.
Nobody is perfect, and nobody is a perfect villain. Try to keep that in mind when you're writing and your characters will be richer for it.
5. You can still write isolation horror (think through your setup).
1977: The Shining is published. The Overlook Hotel sits high in the Colorado Rockies. When winter sets in, the Torrances have only landline phones and a radio to reach the outside world, and a snowmobile to get down the mountain. The phone lines go down quickly, and Jack destroys the radio and the snowmobile as he goes mad. The family is completely cut off.
Now imagine 2013: The Overlook Hotel sits high in the Colorado Rockies. When winter sets in, the Torrances have a landline phone and a radio to reach the outsider world; also Jack and Wendy's cell phones, a satellite phone Wendy thoughtfully purchased beforehand, and full Internet access. They're still stuck with a snowmobile to get down the mountain though.
The phone lines and the Internet go out quickly, and it turns out cell phones don't work on top of a mountain - even if there's a tower nearby, the weather takes it out, and the cloud cover makes the satellite phone worthless. Jack destroys the radio and the snowmobile as he goes mad. The family is completely cut off, even after 35 years of technological advancement.
You've probably seen more than a few recent horror movies where you just have to ask "Why doesn't anyone have a damn cell phone?" It's especially egregious when a simple phone call would be enough to resolve the entire problem, and everyone's batteries have conveniently died because the plot demands it.
The Shining is technically a period piece, but you could set it in the modern day and barely change a thing. Stephen King put a fair amount of effort into isolating the Torrance family and it still holds up. Give some thought to the situation your characters find themselves in, and hopefully it'll hold up just as well.