Write believable dialogue. We read good literature for joy and also with a writer’s eye to emulate good writing. Some reading is useful as a terrible warning.
For the worst dialogue in the world, read any fiction by Ayn Rand.
No one on earth ever spoke as her characters speak. She has a philosophy to push more than a story so there’s a whole lot of preaching going on. That’s why she’s better known as a philosopher today, not a fiction writer.