Editing Your Book
The first thing you have to do is finish your book. If you try to edit it before it is complete, you will waste time and effort, and may not even finish it. Write every day until you get to the end. Don't try to make it perfect the first time around. That's why they call it a first draft.
Tip: Some writers need to edit as they go. If you just can't do it any other way, that's fine. But don't let the editing get in the way of the writing.
Tip: For new authors -- another reason to finish your book first is that agents and editors usually work with books that are completed and free of errors. There are exceptions, but they are rare.
Tip: If you are a published author, and your new book is in the same category as your published books, you can usually present it before it is complete, with a full synopsis and marketing and publicity information included.
Once you have finished the first draft, you are ready to edit. On the first edit, look for errors in logic, characters that don't make sense or aren't needed, and extra scenes that don't move the story forward. But above all, make sure that the book starts in the right place. "Start where things begin to go wrong." -Marion Zimmer Bradley
Use a guide book if you need help to focus on the right things at the right times. Focusing on the bigger things first, then the next smaller ones, then the smallest like spelling and grammar, will help you edit your book more efficiently. See Stein On Writing, by Sol Stein, Getting the Words Right : How to Rewrite, Edit and Revise, by Theodore A. Rees Cheney (new edition coming in June 2005), and Write In Style, by Bobbie Christmas.
Above all, remember that editing your book is just as much a part of the process of writing as the original act of writing is. If you enjoy writing, you should learn to think of editing as an extension of the craft you love.