(Pause for uncomfortable laughter)
Spies and guns: the low-hanging fruit of the American blogger, and not at all what I'm going to talk about today. The second amendment to the US constitution doesn't go where we're going and when you're writing, regardless of your nationality or politics, the one gun you must control belongs to a Russian guy named Chekhov.
"One must not put a loaded rifle on the stage if no one is thinking of firing it."
- Anton Chekhov
Put another way: don't create expectations and then fail to live up to them.
I tend to write very quickly. In the throes of inspiration, I can throw eight thousand words on a page without stopping to eat as long as the waitress keeps refilling my mug. In that kind of literary melee it's relatively easy to drop a thread or mention an object and then leave it dangling. When I'm revising a manuscript (as I am now) the first thing I check for is gun problems.
The most common culprit of this is the tendency to put unnecessary detail into a scene. It's amazingly easy to get so into your own head that you create a scene populated by minutiae that doesn't serve the plot. I'm guilty of this myself and revising for me is often about going back and trying to decide which detail and how much will set the scene without drowning the scene. The danger being that some little bit of detail that you thought was cool at the time will stand out for the reader and take them out of the scene.
There are obvious exceptions to Chekhov's rule. A policeman (at least an American policeman) or soldier will be carrying a gun and you would have to spend valuable time explaining why he isn't. Putting a gun in a scene where they're expected isn't violating Chekhov's rule. Putting one in a drawing room or library and then failing to use it is. Your audience is left waiting for Godot to walk in and shoot someone and they will resist when you try to pull them into a new scene without first resolving that gun on the table.
Of course, this isn't me telling you that you cannot lay false trails, float red herrings, or make the butler look guilty when it was really the cook. All of those instances of false foreshadowing are paid-off when you reveal why the butler didn't do it as you must do in the course of revealing that the cook is lying fink. The payoff is the important part.
Chekhov's "gun" doesn't have to be a firearm. A character leaving bloody fingerprints on the pages of a book was a neat bit of realism for me because he cut himself in an earlier scene, but my beta readers spent the rest of the book wondering when his bloody fingerprints were going to become important. They weren't important, it was just me shooting my story in the foot with Chekhov's gun.
Any character, artifact or plot element that by its very nature, creates an expectation in the mind of the reader will destroy their suspension of disbelief if it doesn't pan out.
I began this post with a sort red herring about guns and Russians and then pivoted away from the current political hot-button issues to a discussion of dramatic elements. No one got past the Chekov quote still expecting me to express an opinion about Russian espionage or the Second Amendment. It might've been a little lame, but it wasn't Chekhov's gun.
Don't annoy your readers or they'll stop reading. And if they stop reading... you might as well stop writing. I hope you didn't stop reading.
As a reward, here's a video I found that brilliantly satirizes the whole concept, and yet manages to effectively illustrate it at the same time (the mark of good satire, in my opinion).