Proofreading
Proofreading is the final check of your book's spelling, grammar, punctuation, and formatting:
Does every opening quotation mark have a closing one?
Does your female main character scratch her face on her husband's bread or beard?
Are your chapter numbers in order without any repeats?
Is the formatting consistent throughout?
Have you got text that is spaced too far apart or smooshed together?
Do you have four lines in a row that all end with the word and?
Are some words badly split at the ends of lines (Mc-Broom)?
Your proofreader is the last line of defense between you and your readers, and they can mean the difference between a 5-star review and one that mentions typos, bad formatting, and missing punctuation.
Do I need copyediting or proofreading?
Samples:
Process
I use at least two monitors when I proofread. That way, I can reference your style sheet as I'm reading to ensure consistency. If I'm editing a PDF file, I use a third monitor for the final Word document and look for things like forgotten returns in the dialogue and words that are hyphenated but shouldn't be.


Page checklist:
words/letters that repeat at starts/ends of lines
hyphen stacks
smooshed lines or ones spaced too far apart
words or lines standing alone on the page
random spaces that line up to cause a distraction
Manuscript checklist:
headings and footers consistent
page and chapter numbering correct
flag any words hyphenated across a page turn
flag misalignment of the last lines on a spread
check overall formatting of chapter headings and section breaks