Writers often speak of the first draft as the place where ideas are found and the later drafts as the place where they are made clear. Cognitive scientists have a similar view: the effort of putting thoughts into sentences shows us which of them are vague. A person who believes she understands a topic may discover, when she tries to explain it in writing, that the steps do not connect.
Revision, then, is not mere polishing of style. It is a second round of thinking, carried out with the advantage of having a complete text to examine. Experienced editors tend to begin with the structure, asking whether the argument moves in a sensible order, and only afterwards turn to word choice and punctuation. Beginners often reverse the order, correcting commas in paragraphs that will later be cut.
The practical advice is modest. Leave time between drafts so that the text looks less familiar, read it aloud to catch awkward passages, and decide what the piece is trying to say in a single sentence before adjusting anything else.