As writers, we can also be our own worst critics. Our standards are different than everyone else’s. Sometimes the prose is not as bad as our minds make it out to be.
Additionally, editing can turn into a vehicle for procrastination. When we’re afraid to start new projects, we waste all our time on polishing pieces that are already excellent. Sometimes we just need to stop. Sometimes we need to give up.
We need to walk away.
So, when do I stop editing? When it's time to move on to the next thing. I'm not being flip, here. As a writer, I'm rather like President Josiah Bartlet in my approach: I'm always asking, "What's next?"
On the novels, I find myself doing three rounds of edits. The first comes after I've set the original, first-draft manuscript aside for a while (no shorter than three months, but sometimes quite a bit longer...I still haven't done first markups on GhostCop (not the actual title) yet). This is when I look for awful inconsistencies to tighten up, awful language to replace, useless words to cut. My goal during this round is always to produce a second draft that is at least 10% shorter than the first. This draft then goes to beta readers.
I seem to have done a great job picking my beta readers, because they always give great feedback in a number of areas, and eventually I apply their critiques (maybe) to the book when I generate a second draft. This is when I really try to strengthen things up, by doing more cutting of extraneous crap and highlighting things like villains and their motivations and the like. After this, generally I do one more edit: a proofread, really, wherein I go through the thing after having a few other people proofread it.
And then, now that I'm fully in the self-publishing gig? That's when I format and publish.
Right now I am in the second phase of edits for The Wisdomfold Path, after which it will be time to give it to proofreaders. But how do I know when I'm done editing? That is the original question, after all.
I am pretty hard-nosed about this: I only go through the book once during this phase, and I just don't get hung up on making every single sentence sing. Because, quite frankly, not every single sentence can sing. Am I a perfectionist? As much as I can afford to be. But I can't take years editing a single book, because I've got other ones that need evicted from my head, too.
What also helps is that I've set built-in deadlines for myself. Sure, I'm self-publishing, which means I don't have an editor's deadline to make, but in reality, I do: it's just that I'm the one setting it. The Wisdomfold Path has to be out the second week of November, because I've promised it to people. For me that's really the only way to make sure I'll do the work: set a date and hold myself to that date. That's a major reason why The Adventures of Lighthouse Boy (not the actual title) is currently on the back burner: had I kept working on it, I would almost certainly be staring down the barrel of missing my deadline for Wisdomfold Path, and that's just not going to happen.
I'm a believer in quotas and hard dates for completion of things, and I am not a fan of partial projects lingering on the To Do list for long periods of time. A coworker of mine, a guy who taught me a lot about facilities maintenance, once scolded me: "You know, sometimes you have to actually put a project to bed." That's pretty true. A whole bunch of partial manuscripts on my hard drive does exactly zero good to anybody. I'm in this to get read, and if you want your books to be read, well...sometimes you have to actually put a book to bed.
(By the way, if anyone's wondering, I'm about a third of the way through this round of edits on The Wisdomfold Path, and then it'll be in the hands of proofreaders. I'll do markups then on the first draft of Ghostcop, and then prep a re-release of Stardancer, on more e-formats than just Kindle and likely to include a preview of Wisdomfold Path. Then, focus will shift to final prep for release, followed by a first draft of GhostCop II, followed by first markups of Stardancer III. Onward and upward! Zap! Pow!!)