Proofreading should be the final step before the book goes to the presses. A misplaced comma or missing apostrophe generally is more embarrassing than anything else, but for some publications, it could cost a lot of money to reprint materials. Oakhurst Dairy learned this the hard way when they neglected to use a serial comma (also called an Oxford comma or a Harvard comma). A missing comma in this case resulted in a loss of $5 million. http://www.cfodailynews.com/why-this-company-is-out-5m-over-a-missing-oxford-comma/.
Proofreading is looking over a manuscript and identifying and fixing any misspellings, punctuation problems, or grammatical issues. Proofreading should only be done right before you plan on publishing your book or article. Proofreading doesn’t consider if the plot makes sense or if the character development is effective; by this time all those issues should have been settled. I have worked with authors who chose not to have their book line edited but who did want it proofread. I don’t recommend doing this; however, if you have a limited budget and have done edits on your book, the very least you will want to do is hire someone to proofread your book. I normally proofread books, stories, and articles in Microsoft Word, but I can also do it in PDF format or as a Google Doc.
When you are ready to send off your manuscript to your publisher or to publish it yourself, you want a second pair of eyes to go over the text. You've become too close to your work and you need an objective expert to go over each word. As Amy Einsohn writes in her book The Copyeditor's Handbook a proofreader must "scrutinize each comma ('OK, comma, what are you doing here? Do you really belong here? Why?')" I will inspect each comma, question each pronoun, query each abbreviation, and investigate each semicolon. I can't promise that I will shine a light in the face of each period and ask it where it was on the evening of June 15, but I will make sure that it belongs there.
What proofreading does:
· Correct spelling. This includes homophones (site and sight; to, too, and two; write, rite, and right) and homonyms (the whale’s fluke, a fluke of luck).
· Fix punctuation. This includes comma splices, quotation marks used for non-dialogue purposes, misused apostrophes, and more.
· Correct grammar. This includes changes in tense, run-on sentences, sentence fragments, incorrect pronouns, lack of subject-verb agreement, and more.
· If I am given the copy that will be sent to the printers, I will look for widows (the last line of a paragraph), orphans (the first line of a new paragraph), and awkward word breaks.
· I will check to see that all tables, charts, and other illustrations are properly and consistently labeled. If the text refers to a chart, I will verify that the chart is on the right page and labeled correctly.
· For magazines and newspapers, I will check to see that the page numbers are correct.
· If there is a table of content, I will verify that each item on the table appears on the proper page.