As usual, these are merely recommendations, not "rules." Every writer needs to stock their own bag of tricks eventually. But here are a few ideas for inspiration:
1. Sustain Suspense – the best way to do this, from my own perspective as an author, is to (at least sometimes) ignore your own outline and let the story tell itself. Naturally some resolutions may require some carefully structured forethought in order to come off as reasonable rather than random. But as long as your characters are well developed, not only in the readers’ minds but in yours, you can write them into situations from which they simply write themselves out. If you as the creator of your own world doesn’t know what will happen next, that sense of anticipation will be contagious.
2. Twist the Plot - seducing a reader into a false sense of security then sucker punching them with a surprise development is not only a reliable way to keep the pages turning, but it’s also pretty much expected by your audience, especially if you’re writing a mystery. The challenge is introducing an unexpected turn of events that doesn’t seem contrived or unrealistic, even if you’re writing a fantasy or science fiction tale. That’s not as easy as it might sound. You will need to stand back and ask yourself, is this credible within the context I’ve created? If you don’t buy it, don’t try to sell it.
3. Kill off a Major Character – fans of the hit TV series The Walking Dead just endured one of the most excruciating cliffhangers in the history of the medium. I won’t give anything away, but suffice to say, while not exactly surprising, the demise of certain key members of the cast in such a gruesome fashion was quite effective. But while very sad, their deaths made sense because of the slow, careful build-up. Of course, since all the characters inhabit an apocalyptic scenario, surrounded by zombies as well as human predators, nobody’s death should be a total shock. But sometimes, they are. The trick here is to keep the audience guessing right down to the wire, so even if the sudden death of a beloved character is disappointing due to the tragedy, it’s not ridiculed for its obvious lack of context and credibility.
4.Reveal Your Hero or Heroine’s Dark Side – as Robert Louis Stevenson famously illustrated in The Strange Case of Dr. Jekyll and Mr. Hyde, we all have a dark side we’d rather hide, even the brightest among us. We just have different triggers, depending on our individual circumstances and unique personalities. While you always want to make your main characters relatable, that doesn’t always mean they have to be likable. At least not all the time. Ironically, that’s what will make them relatable: the fact that they wrestle with inner demons, as we all do. Their foibles are as integral to their dimensionality as a character as their virtues. Just like live human beings. Flesh out your fictional people by rattling a few skeletons in their closets, and readers will ultimately appreciate the honesty, even if they’re momentarily repelled by the ugly truth.
5. Mess With Their Minds Via Alternate Realities – inventing your own world is one of the most enjoyable tasks of the imaginative author (and one of the most alluring aspects from a reader’s POV), especially if your characters are bouncing around parallel universes, a la The Flash. You just have to be careful you’re keeping track of the various threads weaving in and out of various dimensions, or even dreams. Speaking of which, having your character wake up at the end of a story and realizing it was all only a dream – a contrivance exploited on various TV shows, most infamously Bob Newhart – can be really, really annoying to the reader. Unless, of course, that’s the beginning of your story, and the protagonist realizes that they just woke up from a dream within a dream, to quote the famous poem by Edgar Allan Poe.
As long as your readers don't feel like they've been duped, your narrative tricks will indeed be treated like candy by your hungry audience. Just try not to make them sick...cheers 'n' chills!