I read this quote somewhere but forgot who had said it: "I'm a writer, but a great rewriter." For me, writing the draft gets the words out, while revising the draft makes the words sing.
Well, I rewrite either because I thought what I had put originally was pure crap, so I delete it and rewrite it. Or when I go back to revise it, I delete, replace, and/or add more details. This is my method.
Sometimes you might look back and see it's not really in harmony what you're written afterwards. It's quite important to be able to detach yourself from the story and simply rewrite those passages for better or throw them away if you feel they shouldn't be there. Keeping them there just because you need some text is bad.
