Hank, the author of more than twenty books, tells you how to write your story. He believes that stories come from the melding of three elements: getting ideas, story design, and story-telling. Ideas have to come from the author. CREATING STORIES covers the last two.

From Chapter 7 of Creating Stories

Subplots have a number of uses. Here is a list of the main ones.

Distract the reader from the main conflict.
Give the reader a break.
Stretch out the tension.
Build anticipation.
Explore and develop other characters.
Provide foreshadowing.

Let’s explore each one in more depth.

Distracting the reader is a device that can be used in many stories. While the reader is engrossed in the subplot, the sneaky main characters are off doing something that will surprise the reader when she finds out what they did.

Give the reader a break: If the plot is especially intense, the readers will appreciate a break. The subplot gives them a chance to catch their breath and cool off a bit before they plunge back into the main plot.

Stretch out the tension: The subplots also make the main plot seem longer, stretching out the tension.
Build anticipation: This stretching out with subplots will build the anticipation of the reader to reach the climax.

Explore and develop other characters: The subplots can be used to explore less important characters and give the readers insights into these characters.

Provide foreshadowing: A subplot can be used to show a development that seemingly is independent of the main plot, but is actually a crucial element in the climactic scenes.

Subplot example
Here is an example of a simple subplot suitable for a short story. Jim is the protagonist in the story and Harry is Jim’s sidekick After the story gets going and the reader is acquainted with both men, Jim says, “Harry, what’s up? You look like something is bothering you.”

“It’s my mother, Jim. She had a heart attack last night and she’s in intensive care.”

A scene or two later.

“How’s your mother doing?” Jim asked.

“Gonna have open heart surgery this afternoon,” Harry replied.

“Oh, man. I hope she comes through all right.”

Another scene or two passes.

“Is your mother okay?” Jim asked.

“She’s great.” Harry grinned at his friend. “The operation was a success. She’ll be home within a week.”

Harry and his mother’s problem is a full subplot even though we never meet the mother. It characterizes Harry by showing his concern for her health. It characterizes Jim by demonstrating his sympathy for Harry’s situation.

More subplot stuff

Subplots shouldn’t stop the main plot from going forward. By this I mean, don’t insert an entire five-thousand-word subplot in between two main plot scenes. The subplot scenes should be spaced out and interwoven with the main plot and other subplots. A complicated subplot can run for the entire length of the main plot or a simpler subplot can wrap up during a single part of the story.

The subplots can involve less important characters or they can involve the main characters. In this latter case, the protagonist will have two or even three problems to work on. This can lead to overload for the character and greatly increase the tension and his emotional upheaval.

Subplots must be handled in a way that interweaves them with the main plot. In many cases, the subplot will impact on the main plot’s development and either hinder or help that development.

If you have any questions or comments on this material, leave a note and I’ll respond.