“One must not put a loaded gun on the stage if no one is thinking of firing it.” Anton Chekhov
Or, don’t introduce elements that serve no purpose in your story. Purpose doesn’t necessarily mean serving the progress of the plot, or being involved in the dramatic climax. It means that what you put in must enhance the reader’s experience in some way – by developing the plot, directing the action, deepening character, creating powerful atmosphere.
This principle doesn’t just apply to a dramatic object like a gun (the heroine’s karate skills / the rickety bridge over the chasm / the serious contagious illness in the village). It applies to pretty much anything you choose to put in a prominent position.
Let’s take a practical example that’s less obviously plot-directing than a gun. Say you’ve decided your hero keeps tropical fish. Why is that?
Just because. (It sets the scene. Fish are pretty.)
Bad. Go to your room and don’t come out till you can play nicely. I do not want to read five pages of fish-related scene-setting if you then forget all about it and the rest of the book might as well be set in a shed.
Basic character. (It shows my hero is kind of a geek.)
A bit better, though probably a slur against the fishkeeping population. You can use the fishkeeping to show us that he’s meticulous etc etc. Or you could have shown us that in a myriad of other ways and we wouldn’t have had to drag fish into it. I don’t sound excited yet, do I?
Basic plot set-up. (The love interest owns the cat shop next door to the hero’s fish shop. They meet after an unfortunate incident.)
Still not enough. If the only purpose of the fish shop is to introduce the protagonists, it’s a gimmick. You’re using the fish to start action, but not further it. You can do more!
Plot device/character in action. (The hero is supposed to be flying out for a weekend in Paris with his new lover, but his fish-sitter has pulled out at the last minute. Does he go, knowing he’ll come back to tanks of dead fish, or stay, causing a ‘You care more about those fish than about me!’ scene?)
Here we go. Bring in the fish, use them. The fish might be a practical problem – the demands of fishkeeping impact on the hero’s time for his new relationship. It might be a way to reveal backstory/character – why does the hero prefer fish to people? The hero’s changing responses to the fish might show his character development throughout the book. Or it might operate on a more metaphorical level, so that we observe the hero trapped in a small world, going round in circles, just keeping on swimming without going anywhere. (I don’t know, it was your idea to make him a fishkeeper.)
Whichever way, the fishkeeping element should interact with plot and character to move the story on, or tell us more about the people, or ideally both. If it doesn’t do any of those things, it’s just wallpaper: pretty but two-dimensional.
The Scene. (I wanted the hero and his lover talking on either side of a fishtank, looking at each other through the rippling water and shoals of fish, not quite seeing each other clearly.)
Chekhov’s gun doesn’t have to be part of an active developing plot strand. If the purpose of the tropical fish is to create a brilliant, memorable, well visualized scene, or if the aquarium setting broadens and deepens the reader’s feel for the characters and the characters’ understanding of each other, that’s the gun fired. The fish have achieved their point.
Chekhov’s AK-47. (Dead bodies are turning up with still-flapping tropical fish stuffed in their mouths. A brusque yet handsome cop must work with a reserved yet sexy fishkeeper to track down the Tropical Fish Killer before he strikes again.)
I swear to God I’ve read this.
As William Morris almost said, you should have nothing in your novel that you do not know to be useful. If you have an element in your story and don’t know what its purpose is, go back, find out what it’s for, and revise to work it in. If it doesn’t have any purpose, what’s the point?