Self-Editing for Fiction Writers is a great book that covers the basics of editing your own work, or that of others, and how to apply those skills.
Having been involved with editing and writing for a number of years, the book didn't offer me anything ground-breaking, but it did reaffirm my love of editing and brought to the forefront of my brain, the things to keep in mind when reading and reviewing a piece of writing.
The book gives you plenty of examples of poor writing, mediocre writing and some fantastic writing. It hacks apart some of the greats, and showcases some works by authors unknown.
I found the snippets that were edited two or three times in the book to be the most impressive. It really gave meaning to what the book was trying to say. Seeing the process in one paragraph of text really pushed the ideas home and solidified them in my mind.
Not really one on rules, this book is written in the hope it will guide you towards better writing.
If you're a writer but not so good with editing, this should be top of your book wishlist.
P.S. It got my 'editing required' shelf because there's some shockers these pages.