Years ago the novelist and critic E. M. Forster stated in his Aspects of the Novel that there were two kinds of characters. Round characters are those that were multi-dimensional and complex. The kind that lead a reader to believe a character is realistic. Round characters are usually the major characters of a novel, unless the novel is a comedy.
Flat characters are those that are one-dimensional and simple. The are usually the walk-on characters who have only a few scenes. Characters like the cop that gives out a ticket or the cook in a restaurant.
Anne Tyler proved that this didn’t necessary need to be. A walk-on character could be just as round as a major character. In The Accidental Tourist, she has a waitress serve Macon Leary, the protagonist. In just a paragraph, the waitress is as alive as any round character in the novel. The fact that I find her memorable years after reading the novel proves that.
When writing a novel, try to see the walk-ons as real people with real lives. The novel may be the protagonist’s movie. But the walk-on sees themselves in their own movie intersecting with the protagonist’s movie. Sometimes the walk-on becomes so memorable that the novelist feels they have to write a novel for that character.
So give your walk-ons a chance to shine. They won’t let you down.