When I think of symbolism in fiction, I often think of Flannery O’Connor short story “Good Country People.” In it, Joy, a highly educated woman who has renamed herself Hulga, tries to seduce a Bible salesman. Instead, he steals her wooden leg. That leg garners a lot of attention in the story and, as a result, it accumulates meaning. The reader sees it through Joy’s (or, rather, Hulga’s) perspective, as well as the perspectives of her mother and the woman who helps in their home. It’s clear the leg is meaningful; in some ways it defines her. When the Bible salesman steals it, he’s taking something essential.
In her essay “Writing Short Stories,” Flannery O’Connor has this to say about the wooden leg: “If you want to say that the wooden leg is a symbol, you can say that. But it is a wooden leg first, and as a wooden leg it is absolutely necessary to the story.” An aspect of fiction—an object, an attribute, a circumstance, etc—can become a symbol, but it must first be a necessary presence in the story. As you write, let O’Connor’s words echo for you.
In William Golding’s novel Lord of the Flies, a group of young boys are stranded on an island after a plane wreck. A conch is used to summon all the survivors and, as the story unfolds, it becomes an object of power and social organization. Still, it is a conch first—a means of communication, which the boys use, manipulate, and create rules around. Each time they interact with the conch it gathers meaning. Through that process, it becomes a symbol.
Symbolism that appears because you approached it with the intention of doing something lofty is bound to act like a scoundrel. It will announce itself. It will usurp attention. It will supplant the subtleties of characterization and gradually increasing tension.
Instead, write the story with the objects, character traits, and circumstances as they are necessary to the telling of that story. Then, take a look and see if there are possibilities for symbolism. Is there some element that seems to be working beyond the literal toward deeper meaning? If so, has it accumulated enough meaning? Can you coax is out more?
Focus your attention on characters whose actions are fully motivated and who interact with their surroundings in authentic ways. Let symbolism emerge.