One of the books I found most helpful when I began freelance editing was Carol Fisher Saller’s The Subversive Copy Editor. Unlike style guides and other trade references that editors consult more or less daily, Saller’s book focuses not so much on how to copyedit as on ‘how to survive while doing it’.
I’m happy to report that The Subversive Copy Editor was recently published in a second edition. Two chapters longer and noticeably heftier, it still falls well under 200 pages: you’d zip through it in a day or two. It’s full of solid advice on such aspects of the job as managing deadlines, handling pressure and difficult clients, improving your computer use (e.g., filing, word processing), and email etiquette.
It also offers clear and practical guidance on the nuts and bolts of editing. For example, it explains the benefit of reviewing your queries to an author before you return their text: