I wish there was a process. So far, it’s been a haphazard thing with me. I’ve recently settled on one process which seems to be working (for now).
For my novel, I focus on one chapter at a time. If it is a long chapter, I divide it in half. My focus consists of reading each word slowly to myself. If I hesitate, I stop and reword what I wrote. Even if what I wrote was great, if I hesitate then a reader will, too. When I’m done, I read what I wrote a little faster.
I continue this until I have read the chapter without hesitating or making significant changes. Focusing on a few pages at a time is the key along with speaking each word carefully.
A writer must take the time and focus on editing. Not dwell on the editing until the words become like salt in your eyes, but become the reader after being the writer. And don’t rush. Value is more important than speed.
Whether a writer likes editing or not, it is unavoidable and mandatory. Other, broader editing will look at the plot. But specific, focused editing will take the most time and be the most valuable.
Writers should do the majority of editing themselves before sending it to a professional editor. By editing first, the writer has a deeper look at what they wrote. They will understand their work from different viewpoints and angles. When an editor proposes changes, the writer is better equipped to decide what changes to accept.
There is no good answer to when a writer finishes editing. Just don’t let it become an obsession. When changes become fewer or the original returns, it might be a good time to say that’s enough.