I typed this article, ran the spell checker and read it over a few times. The errors serve as an example of why everybody needs an editor. The question for most writers is whether or not they can fill that role themselves. If you are self publishing a book, it would be crazy to cut corners on expenses by not hiring a copy editor, unless you can do a top-notch job yourself.
I’m pretty good editing myself in the hard edit sense, but when it comes to grammar, I don’t know all the rules. I am left to look up the rules on the net. For my recent book, Ricky Robinson Braveheart, I sent if off to a line editor over a year ago, but I did the editing after that.
Both editing and proofreading are true professional callings, by which I mean that hiring several amateurs to do multiple passes doesn’t get you the same quality as hiring one true professional.
Printing your book in the final layout before proofreading will likely improve your accuracy over reading on the computer screen, but I do advise taking advantage of Microsoft Word’s grammar checker and doing at least several passes through your whole document, examining every instance that they underline in green, red or blue. If you right-click on the grammar “errors” you’ll get Word’s explanation for why it may be wrong. I ignore the majority of their suggestions, but it’s worth the time to look. I often realize that I could have worded something better. I don’t run any of my blog articles through Word.
Another trick is to download the Kindle formatted book from Amazon before publishing, and read it on Kindle. The trick in doing this is to look at your book in different formats, which helps to locate errors.