I Writers need different types of editors at different stages of a book writing process.
Structural editors come in closer to the beginning of the job. They look at the whole piece. Whether it's an article, chapter or book. They look at things like "what genre is this?" And "does it flow logically from one section to another." And "Is the author using all five senses to describe people, places and things?"
Copy editors come in at the end of the job, when the draft is nearly ready to send to the publisher. They read every word, and examine at every bit of punctuation. A good copy editor is invaluable., and will save you from embarrassing typos, spelling errors, and convoluted sentences.
Structural editors are harder to find, and their hourly rates are higher than copy editors. It's a good idea to ask for references and samples of previous work. A good place to hire freelance editors is the Editorial Freelancers Association (EFA).
In the last seven years I have written three books that failed. They are unreadable, and in my desk drawer for good. Two nonfiction and one fiction. That's a lot of dollars, time, and sweat, wasted.
So... I stopped writing my current book and asked myself "What am I doing wrong?"
It's not as if I don't know how to publish a book. I've published two trade books since retiring. Before retiring, when I had my technical writing business I planned, researched, wrote, and published over 300 technical books of all kinds for the corporate market.
I decided to assume that I knew nothing, and start from scratch. I began with Google searches on how other people go from idea to published book.
Fortunately I found the website of Marissa Meyer. She wrote a brilliant description of her process of going from idea to finished book.
As I reviewed Meyer's process I realized that when writing commercial trade books and fiction, the second draft process is critical. Meyer writes:
"The second draft is the most complicated stage of my writing process, and half the time I feel like I have to re-learn this part with each new book, but I’ll do my best to break it down into something that seems halfway logical..."
She then explains how she revises her first draft, using Scrivener.
Meyer is the first author I've read who really explains how to revise a second draft, and I have about 150 how-to-write books on my bookshelves. (I collect them as a hobby.)