The hard part about revising a book so that it will be ready to send around to your agent or editor is, trying to make it better without busting something.  This is easier in the age of computers and cut-and-paste than it was back when everything was produced in long hand or by typewriter, but the writer still lives in horror of spoiling something in the process of trying to improve the writing or pacing.  My friend Hershel Parker has written the definitive work on how writers, including Twain, Crane and other giants of literature, came close to destroying their own work in the process of rewriting it so that it would sell or, perhaps, to meet the whim of an editor or publisher.  Hershel's book is FLAWED TEXTS AND VERBAL ICONS and it should be required reading for all writers and editors.

Still, in the case of my work, the book that emerges from self-editing is almost always better than the book was before.  Sometimes, a book can even benefit mightily from sitting in a drawer for a few years, letting it age in the writer's head. That's the case with the one I am working on now, which I first finished in '06.

Beethoven said, genius is the art of taking pains.  I don't know about that, but I do know that taking pains is the only way to make sure the rewriting and self-editing process doesn't do more harm than good.