Foreshadowing is the method by which you drop hints to your reader about something that is going to happen later in the book. Sometimes you want your reader to suspect, and sometimes you want them caught completely off-guard. If you do want them to have an inkling, foreshadowing is what you’re after.
Say, for instance, that Sally is going to die from a drug overdose. In all of her outward appearances, she’s a respectable citizen, choir member, volunteer at the community center, and no one would ever suspect her of being a drug user. When she dies, it’s going to be so unexpected that the reader won’t really buy it. But what if George walks in on her and sees her slip something into her purse, and she’s acting strangely. He doesn’t ask her about it because it’s none of his business, but later, when she’s dead and the drugs are found in her purse, it will make sense to the reader and they won’t feel as left out as they would otherwise.
If you want to do a little foreshadowing but still have Sally’s death be a surprise, you do want to be subtle. You wouldn’t necessarily go through the manuscript and show Sally experiencing all the classic signs of drug addiction unless you wanted the reader to know it all along. Readers are very smart. They’re looking for plot twists. They’ll take each sentence and look for the hidden mystery. If you don’t want them to know, you can’t spell it out.
Let’s say cousin Ed turns out to be a thief. It would be good to have money turn up missing from time to time, maybe an hour or two after Ed leaves the house, or even the next day. If this plot element is a surprise, don’t have it happen every time Ed comes, and don’t discover it until he’s been gone for a while. Put plenty of other characters in there that it could have been, and possibly even more likely characters than Ed.
The #1 mistake authors make when they are foreshadowing is to use the expression “Little did they know.” Poor Aunt Gloria, fretting and fuming over the $20 missing from her purse. She needs it to pay for her heart medication and she can’t imagine what could have happened to it. But little did she know, Ed stole the money, and if she knew, she’d have a heart attack. Of course she didn’t know. If she knew, it wouldn’t be a mystery. When you say something like “Little did they know,” you’re telling the reader things that the characters themselves don’t know, and you yank the reader out of that third person POV you’ve created into a world where the narrator and the reader are sharing secrets. That’s very jarring to the reader and throws them out of the world of pretend.
It’s not difficult to plant subtle clues. What is difficult is knowing when to stop.
SPOILER ALERT: In my book “Strength to Endure,” Anneliese has a crush on Kurt right from the start, but he’s enough older than she is that she doesn’t think he could possibly be interested in her. He’s going off to college to become a professor, while she’s just a girl from the farm. At one point, she tells him that he’s very wise, and he tells her that she’s very young. She takes that to mean that she’s too young for him, but when we see them get together, we read a double meaning into that. He’s reminding himself that she’s too young, and that he’d better keep some distance for the time being.
In summary, to foreshadow, drop vague hints. Show an occasional hole in the character’s armor of secrecy. Give the other characters reason to wonder, but also show holes in the other characters as well. When the big moment of revelation arrives, the reader should be able to say, “Wow! What a surprise! I didn’t see that coming! Although, now that I really think about it, he did come to the Halloween party as Jerry Springer. I see how it all ties together now.”