Question: How do you create entertaining subplots from your main storyline that go well with the main plot, but does not disturb it or overpower it?Answer:
There are several approaches to creating subplots.
Shakespeare, for example, used to create subplots that had the same theme as the main plot, but involved different characters and so presented the issues from a different perspective, social class, etc.
Another approach is to use the some of the same characters as appear in the main plot, but turn their relationship into a subplot.
For instance, you may have a group of characters involved in a particular goal. Let's say they are traveling through the jungle looking for a lost treasure. But while they are on the journey, some of them may come into conflict over a different, more trivial issue, such as who has to do various chores around the campsite each night.
What distinguishes the subplot from the main plot is that the Goal or Problem will be less significant - that is, it will affect/involve fewer characters or lesser characters, or have less of an impact. For instance, the outcome of a war could affect the entire world, whereas the outcome of a poker tournament in the officer's mess may only affect a few officers in one army.
However, to make a subplot entertaining, it should still have a goal, consequences, requirements, forewarnings, characters with conflicting motives, and possibly some of the other basic plot elements. It just may not be as fully developed as the main plot
(See https://www.how-to-write-a-book-now.com/plot-outline.html )
One other thing, subplots often are presented in a different mode of expression. For instance, if the main plot is a serious drama, a subplot might be comedic, and vice versa. If the main plot is about big ideas, adventure, or thrills, the subplot may revolve around about trivial information or opinions. In this way, subplots give the reader a break from the main plot in order to emotionally recharge.