Middle school and high school level English teachers are forever asking students to look for symbolism in the classic novels they read. The assignments are so ubiquitous that you have to wonder how this much symbolism actually gets written into so many great novels. In 1963, 16-year-old Bruce McAllister decided to get to the bottom of that question by writing to 150 novelists and asking them if they intentionally wrote symbolism into their works. He asked four questions altogether, and received replies from many of those authors.
“Do you consciously, intentionally plan and place symbolism in your writing?... If yes, please state your method for doing so. Do you feel you sub-consciously place symbolism in your writing?”
Jack Kerouac: "No."
Isaac Asimov: “Consciously? Heavens, no! Unconsciously? How can one avoid it?”
Joseph Heller: “Yes, I do intentionally rely on symbolism in my writing, but not to the extent that many people have stated…No, I do not subconsciously place symbolism in my writing, although there are inevitably many occasions when events acquire a meaning additional to the one originally intended.”
Ray Bradbury: “No, I never consciously place symbolism in my writing. That would be a self-conscious exercise and self-consciousness is defeating to any creative act. Better to let the subconscious do the work for you, and get out of the way. The best symbolism is always unsuspected and natural."
John Updike: “Yes—I have no method; there is no method in writing fiction; you don’t seem to understand.”
But that's just the beginning. Read what other authors said about this and McAllister's other questions at mental_floss. You have to wonder how many aspiring writers were discouraged by the unnecessary idea that good writing must be infused with symbolism. From what I've seen and read, good writing comes from practice more than anything else.