If I listen to music while I'm writing, I guarantee the music floating from the speakers will be classical. However, writing itself can be viewed as a classical composition.
First are the soloists - your main characters. Each must speak with their own voice and yet blend harmoniously into the piece as a whole. I think about each character's vocabulary and speech rhythms. Is this character well-educated? Are they plain-spoken or crafty? Nervous or confident? Answers give me the right notes.
Surrounding each of your soloists are the other members of the orchestra - your supporting and background characters. Each has an essential role to play but can't draw too much attention to themselves. Tricky. Supporting characters can be loud or showy, but they can't be heard too often or they tend to drown out the soloists. Background characters need for their voices to be heard, but it is a quick moment in the sun. Think of them as striking a triangle, not a bass drum.
Every symphony has its quiet passages and its rising crescendos. Let your story have changes in pace as well, or changes in mood. No one would want to hear the same note repeated for an hour; why should a reader be expected to read the same thing page after page after page?
Composing a symphony takes time, skill and perseverance.