Nothing keeps me reading like secrets. In fact, I might even venture to say that nothing is more important to a good plot than the ability to keep a secret. The delicate art of hiding, hinting at, and revealing secrets is not only the essence of a good mystery or suspense story. It’s also the driving force behind novels of all kinds, all genera—the thing that keeps your reader’s eyes open.
Secrets come in many forms. Commonly, characters harbor secrets: secrets of identity, origin, motives, past conflicts, etc. It’s the author who has the secret of their future, their purpose, their final decision. Settings have secrets: what is this place? What happened here?
You have to decide how much you want to hint at a secret. Sometimes it’s fun to startle a reader by bringing out a secret suddenly that was never suggested, or even appears to contradict evidence that you’ve arranged to cover it. It makes a brilliant plot twist if you can skew information so that it seems to suggest something else, and then later reveal what was really going on.
Hinting, however, is the language of suspense. Some twists and blind curves can be used to surprise your readers out of the blue, but those hints that almost can be pieced together—but not quite—are what gives them a reason to keep perusing the story. Be conscious of how much evidence you put forward, and how often. How frequently you hint at some hidden element depends on how soon you intend to reveal it. If you’ve got a secret you don’t want to reveal until the climax of a novel, don’t bring it up in every chapter. Let your readers forget about it for a chapter or two now and then, and take that time to develop some other subplot. If you keep obsessing over a bit of information you’re not going to reveal until much later, your reader will very likely become impatient with the whole thing. You want your reader motivated and intrigued—not impatient.
Also, don’t give hints that are too obvious. It drives people crazy if an author pretends to know less about something than the reader already found out about. Don’t keep hinting about a secret that’s already pretty much out of the bag.
Sometimes, when you finally do let a secret out, you still don’t have to be obvious. Never over-explain anything. At least, as far as I’m concerned, I like to be able to read a book a second time and marvel at the author’s subtlety. If there’s something I didn’t fully catch onto, I’ll probably go back and figure it out. It’s more fun for a reader to feel like they’ve gotten in on a secret, than it is to feel like they’ve had it all explained to them.