When I was writing my young adult novel, when I finished a scene, after I was reasonably sure the words were just the ones I wanted, that my dialogue was natural, that my grammar and spelling were correct, I would print out the scene, and in my office, alone, like a performance artist, I would act out the scene, reading out loud, using the voices of the narrator and each character. If someone had seen me they would have probably thought I was nuts. But this was a sure fire way of finding out what sections of the scene needed work.
Reading a piece of fiction or poetry out loud, you hear it with the ear of the reader. Sentences that need pauses, words that require inflection or emphasis, the dialogue between two characters, rise up off the page in a way they simply can’t do by reading the work silently.