Self-published authors are constantly getting the advice to "hire an editor" before they publish. This is great advice. GREAT ADVICE! If you do not do this you should "go directly to jail; do not go pass go, do not collect $200" on your way. Period. End of story… or is it?
Personally, I don't think hiring just a copy editor goes far enough. Not only do you need an editor to go through and make sure your grammar and punctuation are correct, but you also need, what I call, a CONTENT editor (sometimes called a development editor). Which is usually a whole different kind of animal and skill set from your regular editor (not always, but often enough).
So what is a content editor? Find out what a content editor is here.