Cliffhangers are an effective writing trick, and fans of the Deck of Lies series know I love using them. But there's a dark side to using cliffhangers in fiction. Don't let it take you by surprise, or lull you into using cliffhangers indiscriminately.
What Goes Up...
At the end of a chapter, a cliffhanger leaves the reader hungry for more -- and it compels them to keep reading when they might decide to close the book otherwise. Readers want to be thrilled, they want to feel suspense, they want the tension and the drama. Cliffhangers are a very suitable way to give them all of that, but like all good things cliffhangers have to be used in moderation...and sometimes, they shouldn't be used at all.
It's important to include some natural stopping points in any book, because no one can read all the time. Ideally, your readers will read your story all the way through without putting it down once...but that's not always possible. Natural pauses and stopping points aren't just convenient, they help to relieve the tension you've been creating.
You've always got to relieve the tension, even if you wait until the sequel to do it. Every reader, every person, has a breaking point. If you keep them hanging out on a cliff and leave them with their tension for too long, they're going to snap. Usually, they'll just get frustrated and stop reading your book. But even if they do finish it, they aren't going to be satisfied with anything from that point on; that's what a breaking point is. Too much tension and too much waiting will force a snap, and it's in those moments that bad opinions are formed. You can't overcome that, even if the writing that follows is phenomenal.
Ending chapters on cliffhangers is common, and it's a good way to keep compelling your readers along through the book. Relieve the tension in the next chapter, either quickly or after you've drawn the suspense out a little, to keep the story moving and keep the reader happily engaged in the tale.
Ending entire books with cliffhangers is a little bit trickier.
The cliffhanger ending is immediately frustrating to any reader, because everyone wants a complete story when they sit down with a book. However, when it's done well the cliffhanger ending is also enticing and thrilling, rife with the promise that another book (and more of the story) is on the way.
So make sure you're ready to write the next book. You don't want to keep your readers on the hook for too long waiting for a cliffhanger to resolve. If the cliffhanger isn't resolved in the next book (if, for example, you're writing a multi-book series), you've got to make certain that some sort of progress is made. Readers want answers, so give them some even if you aren't giving them the main answer they want. Dragging a cliffhanger out too long can seriously dampen enjoyment of any story, and leaving too many unanswered questions is like shooting yourself in the foot. If you let it go on too long and drop too many hints, your readers are going to figure it out before you're ready and then there's no reason to keep reading.