If a story is a train track, a subplot is the trestle. The main plot takes you where you need to go, from point A to point B and all destinations in between. But without the subplots, it would never make it over the valleys that inevitably manifest during a story arc.
Some people define story as characters acting within a setting. I’ve never totally bought in to that, but I do believe that characters generate subplots. Whether you are a pantser or a plotter, your characters have histories and quirks that lead them in certain directions, giving birth to subplots.
A good subplot tells us things about characters that we need to know in order to strengthen the main plot. It helps develop three dimensional characters, and encourages showing rather than telling.
The subplot must enhance the main plot. It intensifies the emotional catharsis. It elevates the jeopardy, and with it, the pay off. A trestle must be connected to the track in order to support it. A subplot must connect to the main plot, otherwise it is worthless.
Subplots are magical creatures. They grow organically as you learn about your characters. Sometimes, they are more fun to write than your main plotline. You haven’t spent nearly as much time thinking about them. They are fresh. They are new. They are sexy.
Part of writing, especially if you are a pantser (a seat-of-the-pants writer who makes up everything as you go along), is that you’ll occasionally stumble upon a subplot stronger and more interesting than your main plot. When that happens, you have a couple of choices.
You might keep plugging ahead, and see how it all turns out. On the other hand, you could take that subplot and make it the main plot. A story is a world. All sorts of things are happening based on cause and effect. You can’t focus on it all at once. Anne Lamott described writing as looking through a one-inch window. Lamott reminded herself that all she needed to write about was what she could see through that window.
If your subplot is more story-worthy than your main plot, nothing says you can’t shift your attention to it. You might use it to write a totally different story. The important thing is that your sub-plots empower your main plot, not overpower it.
A good way to develop ideas for subplots is by writing character biographies. Characters’ histories lend themselves to continuation through subplots. There is always a reason why people are the way they are and do the things they do. Those reasons can be sub-plot inspiration.
Flash fiction doesn’t require much, if any, sub-plotting. Short stories usually have hints of sub-plot, but they don’t require much attention. However, if you are going to sustain a reader for the duration of a full-length novel, you are going to need subplots. They are the sideshow that keeps the reader entertained while you stage the elephants in the main tent.
Don’t be afraid to give your subplots a little bit of attention. They will give depth to your story, and incorporating them will make you a more skilled writer.