After my mother read my latest first draft, she said those words, the words no writer should take to heart. The words which are the absolute worst advice that a writer can follow--with one exception. Now, these weren't bad words, or mean words. My mother is a great fan of my work, as mothers should be. And she was quite pleased with the story. She offered me praise, and as praise, they are very nice words. But followed? Never. Well, hardly ever.
The one time that the advice should be followed, the only time that any writing advice should be followed blindly, is when it is accompanied by the words: "I'll get a contract right out to you."
And the advice? "Don't change a thing."
Never, never assume that your writing is so perfect that it cannot be improved upon. Never, never assume that you have written your story the only way that it can be written, or that your words are the best you can do. Writing is an exercise in creativity, and creativity is best found in flexibility. You should shift things around, experiment with more words and less words, and even examine scenes from other points of view. And if you keep backups of your work, you need not fear losing anything.
Spend some time working with the story.
Yes, at some point you will have to declare it finished and stop fiddling with it--if not out of consideration for your readers, then so that you may move onto other projects. Declaring a project finished too soon means that you will not get a chance to grow, explore, develop. Don't waste the opportunity. Tell your readers "Thank you," assure them that will you stay true to the vision in the book, and get back to work.
So if saying "Don't change a thing," is such bad advice, why do readers do it? Because they aren't giving you advice. They are giving you praise. They are telling you that the big picture worked well for them, that they enjoyed it. But they really don't mean, "Don't change a thing." After all, even my mother's statement was followed by, "And I've made up a list of corrections and questions that I have."