Amazon.co.uk
I've read quite a few books about writing, and I have to say that this is potentially one of the most helpful and useful. I will quite cheerfully admit to having no idea as to how to go about editing my manuscript properly and professionally, and after the debacle that was the 'Editing' class I went to at the university (don't ask), this was a breath of fresh air. And, dammit, cheaper than that class was, too!
Browne and King not only have an engaging, easy-to-read style, but make their points clearly and succinctly, showing you the different options rather than just telling you (aha!) While they don't dive into the 'bigger picture' aspect of editing - as this would differ hugely between books - they do make many good points that will help with that, as well as fixing all the smaller problems that really niggle with readers when they're left alone.
Many published authors say that they sit with this book by their elbow whenever they start revisions, no matter how many books they've written and sold. I'm perfectly willing to do the same.