There is an article on suspense in the Writer’s Digest online blog by Steven James, one of the Writer’s Digest editors, that was recently featured but dated nearly seven years ago. He discusses six techniques for crating and sustaining suspense, which I think are quite good.

“1. Put characters that readers care about in jeopardy
Four factors are necessary for suspense—reader empathy, reader concern, impending danger and escalating tension.
We create reader empathy by giving the character a desire, wound or internal struggle that readers can identify with. The more they empathise, the closer their connection with the story will be. Once they care about and identify with a character, readers will be invested when they see the character struggling to get what he most desires.
We want readers to worry about whether or not the character will get what he wants. Only when readers know what the character wants will they know what’s at stake. And only when they know what’s at stake will they be engaged in the story. To get readers more invested in your novel, make clear: 1) What your character desires (love, freedom, adventure, forgiveness, etc.); 2) what is keeping him from getting it; and 3) what terrible consequences will result if he doesn’t get it.
Suspense builds as danger approaches. Readers experience apprehension when a character they care about is in peril. This doesn’t have to be a life-and-death situation. Depending on your genre, the threat may involve the character’s physical, psychological, emotional, spiritual or relational well-being. Whatever your genre, show that something terrible is about to happen—then postpone the resolution to sustain the suspense.
2. Include more promises and less action.
Suspense happens in the stillness of your story, in the gaps between the action sequences, in the moments between the promise of something dreadful and its arrival.
If readers complain that “nothing is happening” in a story, they don’t typically mean that no action is occurring, but rather that no promises are being made.
Contrary to what you may have heard, the problem of readers being bored isn’t solved by adding action but instead by adding apprehension. Suspense is anticipation; action is payoff. You don’t increase suspense by “making things happen,” but by promising that they will. Instead of asking, “What needs to happen?” ask, “What can I promise will go wrong?”
Stories are much more than reports of events. Stories are about transformations. We have to show readers where things are going—what situation, character or relationship is going to be transformed.
3. Keep every promise you make.
In tandem with making promises is the obligation of keeping them. The bigger the promise, the bigger the payoff.
When stories falter it’s often because the writers didn’t make big enough promises, didn’t fulfill them when readers wanted them to be fulfilled, or broke promises by never fulfilling them at all.
Here’s a great way to break your promise to the reader: Start your story with a prologue, say, in which a woman is running on a beach by herself, and there are werewolves on the loose. Let’s see if you can guess what’s going to happen. Hmm … what a twist this is going to be—she gets attacked by the werewolves! Wow. What a fresh, original idea that was.
How is that a broken promise? Because it was predictable. Readers want to predict what will happen, but they want to be wrong. They’re only satisfied when the writer gives them more than they anticipate, not less.
Make big promises. Then keep them.
4. Let the characters tell readers their plans.
I know, this seems counterintuitive. Why would we want readers to know what’s going to happen? Doesn’t that give the ending away?
I’m not talking about revealing your secrets or letting readers know the twists that your story has in store. Instead, just show readers the agenda, and you’ll be making a promise that something will either go wrong to screw up the schedule, or that plans will fall into place in a way that propels the story (and the tension) forward.
Simply by having your characters tell readers their schedules, you create a promise that can create anticipation and build suspense:
• “All right, here’s what I have lined up for the rest of the morning: Follow up on the fingerprints, track down Adrian, and then stop by the prison and have a little chat with Donnie ‘The Midnight Slayer’ Jackson.”
A story moves through action sequences to moments of reorientation when the characters process what just happened and make a decision that leads to the next scene. We do this in real life as well—we experience something moving or profound, we process it, and then we decide how to respond. Problem is, in those moments of reflection, a story can drag and the suspense can be lost. During every interlude between scenes a promise must be either made or kept.
And, if you resolve one question or plot thread (that is, you keep a promise you made earlier), introduce another twist or moral dilemma (in other words, make another promise).
When a story lags it’s almost always because of missing tension (there’s no unmet desire on the part of the characters) or not enough escalation (there’s too much repetition). To fix this, show us how deeply the character wants something but cannot get it, and escalate the story by making it even more difficult to get.
5. Cut down on the violence.
The more violence there is, the less it will mean.
A murder is not suspense. An abduction with the threat of a murder is.
The scariest stories often contain very little violence.
And, of course, different genre elements dictate different means of suspense. In a mystery you might find out that a person was beheaded. This occurs before the narrative begins, so the focus of the story is on solving the crime. If you’re writing a horror story, you’ll show the beheading itself—in all of its gory detail. If you’re writing suspense, the characters in the story will find out that someone is going to be beheaded, and they must find a way to stop it.
Reader expectations, and the depth and breadth of what is at stake in the story, will determine the amount of mystery, horror or suspense you’ll want to include. Nearly all genres include some scenes with them. As a writer, it’s vital that you become aware of how you shape those sequences to create the desired effect on your reader—curiosity, dread or apprehension.
Also, remember that valuing human life increases suspense. Because readers only feel suspense when they care about what happens to a character, we want to heighten their concern by heightening the impact of the tragedy. Show how valuable life is. The more murders your story contains, the more life will seem cheap, and if it’s cheap, readers don’t need to be concerned if it’s lost.
6. Be one step ahead of your readers.
Here are some ways to amp up the suspense:
→ As you develop your story, appeal to readers’ fears and phobias. (Phobias are irrational fears, so to be afraid of a cobra is not a phobia, but to be afraid of all snakes is.) Most people are afraid of helplessness in the face of danger. Many are afraid of needles, the dark, drowning, heights and so on. Think of the things that frighten you most, and you can be sure many of your readers will fear them as well.
→ Make sure you describe the setting of your story’s climax before you reach that part of the story. In other words, let someone visit it earlier and foreshadow everything you’ll need for readers to picture the scene when the climax arrives. Otherwise you’ll end up stalling out the story to describe the setting, when you should be pushing through to the climax.
→ Countdowns and deadlines can be helpful, but can work against you if they don’t feed the story’s escalation. For example, having every chapter of your book start one hour closer to the climax is a gimmick that gets old after a while because it’s repetitious and predictable—two things that kill escalation. Instead, start your countdown in the middle of the book. To escalate a countdown, shorten the time available to solve the problem.
→ As you build toward the climax, isolate your main character. Remove his tools, escape routes and support system (buddies, mentors, helpers or defenders). This forces him to become self-reliant and makes it easier for you to put him at a disadvantage in his final confrontation with evil.
→ Make it personal. Don’t just have a person get abducted—let it be the main character’s son. Don’t just let New York City be in danger—let Grandma live there.
No matter what you write, good prose really is all about sharpening the suspense. Follow these six secrets, and you’ll keep your readers up way past their bedtime.”