What Do You Need To Accomplish?
The first step is to think about what you need this secondary plot to accomplish. You know the goals and thrust of the main plot, but what will this secondary one do to either aid or impede your main character's objectives?
Next, decide how this secondary plot line should end relative to the main plot. When your reader reaches the end of the subplot (which might occur before, simultaneously, or after the main plot is resolved), they need to feel that the subplot is complete, based on its own merit. But it also has to connect to the ending of the main plot as well, likewise in a satisfying way.
Understanding how the subplot relates to the main plot will help you decide what kind of subplot is it: Romantic, Conflicting, Expository, or Supporting. The next step is to think about your characters' goals.
Multiple Goals; Multiple Plots
Main characters often have more than one goal in a novel.
For example, in The Hunger Games, Katniss wants to:
- survive the Games (Main Plot)
- keep Peeta from being killed
- fight back against a corrupt government system
- further her romantic connection with Gale
Many of the scenes in the novel work to get Katniss closer to several of these goals at a time, while always keeping in mind that her first and most important motivation is to survive.
Once you understand what you need this subplot to do, think of the smoothest, easiest way that can happen—and then break it. See if you can do it the opposite way, or in a way that really screws up your main character and their narrative. Forget easy and brainstorm for interesting.
Going back to The Hunger Games as an example, let’s remember the scene where Katniss gets her nickname, "the Girl on Fire." She and Peeta make a political statement in the chariots when their clothes catch fire (subplot C), garner admiration from potential sponsors (plot A), and further the ruse that they’re in a romantic relationship (subplot B). This, however, complicates Katniss’ relationship with Gale (subplot D) in a delicious, interesting way.
Play With It
I recommend using some form of external graph or software to help you play with the possibilities — if you're more of a hands-on planner, write down possible plot points or scene ideas on colour-coded recipe cards and tape them to the wall or pin them to corkboard; organize plot points on post-it notes; get different coloured markers and fill a whiteboard. StoryBilder can help you do this without burying your kitchen table under a leaning tower of notes.
However you choose to externalize your thought process, study your subplot and look for ways to add complexity. You'll want to examine your main and subplot arcs or your character arcs (or both, if you’re feeling very organized), so that way you can easily see how they interact with each other and where the gaps are when you stand back and examine your full plot map as a whole.
If you’re a Pantser who prefers not to organize so rigorously before you begin to write, I recommend reviewing your main and subplots after your first draft. This process will give you a clear understanding of the narrative you’ve created and help you focus your efforts during your second draft revisions.
Go back to our last activity where you thought about your favorite fairy tale and how you might create complexity. Try mapping out the main plot by writing down the main actions in the story. Now add a second plot line that reflects the new story elements you devised.
Pay attention to ways the secondary plot integrates with the main plot, for example by presenting new information that adds depth to the main story, actions that conflict with the main character's objectives or create new challenges, or develop secondary characters in ways that contrast the main character's journey.