I don’t care if you’re a Pulitzer Prize winner; I don’t care if you head the English Department at Yale or Princeton; I don’t care if you were raised by Grammar Nazis. You need a good editor for your book, someone with a fresh set of eyes and a talent for zeroing in on that misplaced modifier, dangling participle, misused comma, point-of-view error, awkward syntax, and a hundred other problems.
I’ve seen some writing that should never have been published simply because it looked like a rough draft that had never been edited or proofread. If you’re a self-published author, this is not the place to save some money. It will cost you. Take your marketing money and find a good editor. After all, there’s little reason to spend money to market work that, at best, is rough and unpolished and at worst is a piece of crap. I’m sure there are some projects where editors deserve a co-author credit!
I have been extremely fortunate to have had a wonderful editor for the three novels I have done through World Castle Publishing. Her name is Maxine Bringenberg and she has made everything I’ve written better. Much better.
Find a good editor before you publish your book. It makes a difference.