I'm involved with editing for a fellow author. I only started because we had so much trouble finding editors for squick material ("MM", not poop or watersports). However, I've noticed a few things which might help others.
I'm learning a tremendous amount by concentrating on editing others writings. I've got to admit, I make more red marks than any volunteer editor I've ever used (but still much less than my single professional editor made in my own work). It's especially surprising since I rarely make that many substantial changes in my own stories.
Just as there are different types of editors: content editors for the heavy lifting, proofreaders for typos and beta-readers for reader impressions, having a fellow author review your work allows them to focus on the storytelling specifics, rather than the rules of grammar or proper English. When I edit someone else's work, I concentrate on what works, and how they can convey the same information more efficiently (more impact, less verbiage and of course, more showing and less telling). I know, I know, given the length of this message, you can't imagine my making anything shorter, but I've learned to cut my writing down substantially over time.
Unfortunately, while I fill the page with red marks, it also takes an inordinate amount of time (since I also tack on dozens of comments to explain what I'm doing). For those of us already working on multiple stories, it's hard to dedicate that much time, or to do it in a timely basis.
That's why most authors limit their volunteer editing efforts.
When I started, both Switch and Ernest took me under their wings, not only pointing me in right direction concerning my writing, but also explaining about which tools I should use, and how to be more productive.
They both quit after only a couple chapters, but that effort was invaluable, as it saved me valuable time learning those details on my own, and I internalized much of their advice. In my own case, I'm hoping the author I'm helping will pick up what I'm trying to convey about writing effectiveness (saying more with less), so his future stories will take less editing in the end. But for now, I hate cutting him loose mid-story (he'd already finished the revision process, so he was unlikely to rewrite the story).
That's a very long-winded summary to a basic appeal for more authors to volunteer to edit for other authors, especially newbies who need guidance on a number of fronts. We may not know which rules of English we're violating, but we do recognize which approach makes for easier reading.
I'd also like to suggest developing local author groups. I'm not suggesting finding other authors who live nearby, as I've found there's little that autobiographical or non-fiction authors can do for novelists over coffee, but instead, each author should find other SOL authors who write similar works. That way, if you run into story issues, you can ask a 'friend' to look it over for you, and give you a different alternative for how to resolve the issue. I had this relationship with an author when I first started, unfortunately after he died of cancer, I never cultivated new writing support groups (beyond the normal author/editor relationships).
That said: if anyone is starting out and unsure what they're doing, drop me a line. I'll help get you started, at least. What's more, if you're writing something that others aren't volunteering for, again drop me a line. I won't be able to volunteer for long, but we authors can often get you over a hump and fill-in for each other when a stories subject matter isolates us (since, as authors, we're focused on the story, rather than the subject matter).
Anyway, sorry to rant, but I thought this was a worthwhile subject to broach. Here's hoping a few more experience authors volunteer to nurse new talent along. (Which isn't to suggest we replace the need for editors, since we're offering an alternative form of editing!)