Side characters are very valuable. They give depth to the story as well as offer more angles for it. They offer chances for the plot and other characters to grow and show dimension. You can have a story with only a character or two, but you need more than that if you really want to show depth in what you want your readers to see.
So, how do you develop side characters?
First, you have to decide how you want them to be presented in the story. What role will they play? Are they characters who are to show up to help guide the main characters? Yes, that is a role they can play. People don’t just make decisions for no reason at all. Look at your own life. Your life is not unaffected by those around you. Even those who are only there for a moment can help you make life changing decisions. Those are the side characters in your life. They are there impacting your life while not living the main course you are riding.
Think of how the side characters in your life impact you. One teacher who inspired you is not a main character in your story. They are a side character that had a big impact. The bus driver who always smiles and helps you have a good day each time you see him is a side character impacting you. They are important to your story though they are not main characters. See what I’m getting at?
Side characters can be extremely important to a story. They need to be developed almost as much if not as much as the main characters are. What is their own past? How does it impact the story? What aspects of their personality can help create the story you are looking for?