I was thinking about some of the turns in Falling's plot recently, ruminating on how they evolved, grew and took shape, especially the really big one about Vicki and whether she has some prior relationship to what's going on in the story (I won't say either way as I figure this blog should be pretty spoiler free).
But there are tons of them throughout the story because in the last rewrite I built in a lot of set-ups, callbacks and resolutions that crisscrossed between times and characters.
A good example was the killswitch code, a command Dale figures out he can send to the brace to shut it down completely which he intends to during the climax if Tim's idea about changing the field frequency of the brace doesn't work.
The tricky dance around including it was that I had to introduce the concept, but I couldn't do it then and there because it might as well have been wearing a day-glo T shirt that said 'DEUS EX MACHINA'. That meant it had to come up in conversation much earlier, and that meant it had to be something that wasn't just innocuous but was related to something else in the story, otherwise it would be wearing a different T shirt that said 'THE AUTHOR DOESN'T WANT YOU TO KNOW BUT THIS IS GOING TO BE IMPORTANT LATER!!', and nothing yanks you out of any story faster than seeing the author/screenwriter trying to pull a narrative trick on you.
All of which had me thinking about foreshadowing, and how hard it is to do well. And it's hard to do well for just one reason – your audience is always smarter than you give them credit for. if you have a secret you want to reveal in stages and give little hints and clues to it throughout your book or script, I find a general rule of thumb it to make it 25 percent as obvious as you initially think you should (as a maximum – if it's 10 percent they'll still get it).
Because as an audience, we've seen it all. How many times have you watched comic hijinks in a romantic comedy and rolled your eyes because of how obviously it's going to happen? How many times have we seen the hero sent forth from a corporate or institutional infrastructure to root out some criminal corruption only to find it starts at the top of the tree from whence he/she came?
There's nothing inherently wrong with those plot turns (although I do find those old chestnuts incredibly tiresome and I'm convinced writers should/could try harder and really surprise us), but it's the foreshadowing that telegraphs them from the rooftops that really irks us.
If you have a twist and you want to pepper clues to it throughout your story so the reader slaps his/her forehead and says 'Of course! Why didn't I see that coming!', tread incredibly carefully. Strip back and back and back some more. It'll mean the difference between genuine delight and surprise and a groan of boredom that might cause them to close the book and discard it altogether.