Suspense isn’t so much about “making things happen” as it is about promising that they will. It’s more about creating worry, apprehension, and anticipation than it is about adding more action. When readers are bored with a book or when they complain that “nothing’s happening,” they don’t usually mean that nothing is occurring but rather that things aren’t escalating. We solve this problem not by adding more action but by making more promises.
In a mystery you might have someone beheaded before the book begins and the detective (or team of detectives) must work to solve the crime. In a horror story you might show the beheading in all of its grisly detail. In suspense, readers learn that someone is going to be beheaded and the protagonist must try to stop the crime before it occurs. See the difference? The first (mystery) appeals more to intellect—it’s a puzzle that needs to be solved. The second (horror) deals with a more raw, visceral gut-wrenching reaction. We’re not kept in suspense, we see the horrific detail. It’s almost like we’re afraid to look because of what we are being shown.
Suspense, however, deals more with the emotions. It appeals to the concern of the reader for the wellbeing of the character/s. So instead of being afraid to look, readers are afraid to look away because they’re afraid they might miss what is going on.
When readers care about a character and that character is put in peril, suspense is born.
Now, how do we make sure that we don’t lose the interest of readers? How do we make sure that we don’t move too slowly? I have a maxim that directs all of my writing endeavors—always give readers what they want or something better.
So, as I work on my story, I make promises of things that will go wrong (a killer might threaten or abduct someone; terrorists might develop a weapon, hack into a computer, leave a ticking bomb, etc…) then, as I write, I continually ask what the readers want, and I give it to them—or try to surprise them with something better than they ever imagined.
The keys to pacing include making and keeping promises when readers expect them, relentlessly escalating the tension of the story, raising the stakes, and balancing the amount of exposition so that it occurs after climactic scenes when readers wants a break and need a chance to reorient themselves for the next scene.