Editing is the art of nudging and tweaking the words you’ve written, so they become the words you really meant.
A good editor will have you saying yeah, that’s what I meant but couldn’t find the words for. A good editor will not squeeze your writing into a set of rules, running it through a propriety-wringer to make sure you’ve never said something with character or passion. A good editor can enhance and more deeply focus character and passion, crystallizing the writer’s voice.
As much as it pains me to say it, you should not edit your own writing.
Sometimes writers can’t step away from their writing enough to see the lack of clarity here, or the awkward or powerless wording there. Your Elements of Style will only get you so far. Eventually, it’s just better to have someone who knows writing, but not your subject, to give it a solid once-over.
Again, the editor should offer suggestions and recommendations. You should be free to accept or reject. This is your book and should speak with your voice, not theirs.
There will probably be some back and forth in this process before it’s done, but once it’s done, your book is written. Go, you.
Now it’s time to take your words, and turn them into a bona fide book thing.