Secondary characters are not merely sidekicks. Nor should they be yes-men to protagonists. They don’t get the same page time as your main characters, but they should feel like fully rounded fleshed-out people in their own right. When handled correctly, your secondary characters can actually help drive your novel—can be part of the catalyst for change for your main character.
A few things to think about as you round out your secondary character:
1. Ask yourself how they’re different than your main character. In juvenile fiction, your secondary character’s probably going to be a best friend—so there are going to be large areas of overlap. Your MC and a close secondary character will be like-minded and in the same place in their lives (the second grade, the same baseball team, etc.) But: How are they dissimilar? How will those differences allow the secondary character to challenge the main character—either push them farther from their goal or allow them to get closer to succeeding?
2. What personal trial does your secondary character face off the page? If your secondary character is a fully-rounded person, they obviously have their own challenges that have nothing to do with the protagonist. Ask yourself: if this character were starring in their own novel, what might it be about? Probably the most obvious example in my own work of giving a secondary character a problem away from a novel’s protagonist occurs in my YA A BLUE SO DARK. My secondary character (the protag’s best friend) is a teen mother.
3. How does the relationship between the protagonist and secondary character change throughout the book? Secondary characters may not be with your protagonist at the end of the book. Their friendship may be tested to the point that it breaks. How does this impact your own main character’s journey? Does your secondary character essentially start out being an ally then become an antagonist? Does the opposite happen?
Secondary characters are far more than just sounding boards or cheerleaders for your main character. By fleshing them out, they can also provide opportunities for unexpected plot twists as well as plenty of opportunities for your main character to grow.