Let's get some terms straight. When you say you need an "editor," what do you mean?
If you're looking for someone to help you shape your manuscript into publishable form--by advising you about your readership, your content, and your structure--you might be looking for someone calling himself or herself an agent, a writing coach (or consultant), an editing coach (or consultant), an acquisition editor, a substance editor, or a plain old "editor." When I ran the editorial department at an independent publishing house, my title was "editorial director." However, my job could have been defined as "acquisition editor." I helped find, develop, and shape books into publishable form.
If you already have a publishable manuscript--and don't need someone monkeying with the substance--you almost certainly need a copy editor. This is a professional who cleans up the grammar, removes redundancies and writing tics, checks spelling and punctuation, establishes consistent capitalization, and so on.
Many authors tell me they don't need a copy editor because they've had someone, or several someones, "look at it." If you really don't care, go for it. However, you probably will care when your readers and friends begin pointing out boo-boos, tics, characters whose names are spelled different ways or whose names change altogether, and so on. (For some reason, the same friends who won't read an early draft for you seem to be the ones who take particular delight in reporting problems after the book is published.)
Copyediting is not for amateurs--a category that can include fellow writers, English professors, journalists, bloggers, tech writers, the severely anal member of your book club, and others who think (with good reason) that they know their way around the English language.
While some aspects of self-publishing lend themselves to the do-it-yourselfer, copyediting is not one of them. For one thing, you shouldn't copyedit your own work. You've been through the manuscript too many times; you're jaded; and you're not objective. For another, it's just, well, hard.
- It's hard emotionally, at least is is for me. It's a rather intimate exercise, forcing you to spend hours inside the brain of someone else. I can only do it for about an hour at a time.
- It's hard technically. You have to be familiar with myriad grammatical rules and their variants, spelling (and when to look up a word), and style issues. Much of copyediting is about consistency, which requires relating all the details to the whole. Whereas good page-making software forces consistency with style tags, there is no such tool for copyediting. The copy editor is on her own.
- It's hard artistically. For me, copyediting is akin to sculpting. You use your technical expertise to carve away what doesn't belong and expose what is good. The result should in some ways (at least in the best sense) look more like the author than the original manuscript.
- I follow a master style guide.The Chicago Manual of Style is incredibly complex, but it is the gold standard for the book publishing industry.
- I follow a master dictionary. My current one, Webster's Ninth Collegiate Dictionary, Ninth Edition needs to be updated.
- I create a supplemental style sheet. Publishers typically create an in-house supplement to their master guide (e.g., The Chicago Manual of Style), but I've found I need to create one for each book. The supplement itemizes any style variations from the master; lists peculiar spellings; lists proper names of people, places, and organization (to enforce spelling consistency); capitalization peculiarities; abbreviation issues; and so on.
- I do a sample edit before proceeding. I use this to get feedback from the author. This helps me determine how aggressive or lenient to be with my copyedit and identifies any issues that need to be noted on the supplemental style sheet.
- I give my edited copy to the author for their amendments and approval. Eight years ago, when I bought the book-production business that evolved to The Publishing Pro, LLC, copyediting was done in pencil, with author amendments written over the top. The approved changes then had to be transferred to the electronic file. Today I do my copyediting in Microsoft Word, with the "tracking on" so that authors can see my edits. I then produce a clean version--with the changes accepted, the tracking turned off, and the clean file checked against the "tracking" file. This catches more mistakes and nits, with help from Word's grammar and spellchecker. I give both the clean file and the "tracking on" file to the author, encouraging him or her to use the clean file for author alterations or corrections, which should be highlighted in color.
- I review the author alterations. The idea is to make sure they conform to the established style and that no errors have been added. At this stage, I go with the author's wishes unless there are obvious problems.
- I read the page proofs on hard copy before sending them to the author. This is the place where I choose to read the book on hard copy, which is the best way to catch small errors. However, I consider this more of a continuation of the copyediting phase than a proofreading. The copy editor shouldn't be a designated proofreader (a different function), for the same reason the author shouldn't.