I'm suggesting that each of my students create a style guide of their own in which they note writing errors that they tend to make. Once they are aware that a particular habit is construed by me as an error, they can chose to use it if they are writing creative prose.

That's awesome. "Know your enemy."

Few university students have had detailed feedback on their writing. The first real feedback I had was from my thesis advisor in graduate school.

And that's terrifying. Does nobody diagram sentences anymore? Granted, I've always just sort of had a knack for it and sucked when I had to explain what participle phrases were, but some people can dance, I can string words together. Nonetheless, it was bloody beaten into our heads in 3rd, 4th, 5th, 6th, 7th, 8th and I finally broke free in 9th when they determined that Honors courses didn't have to put up with that shit. Then when I got to college they waived English for me so I dunno what that looks like; I had to take tech writing for engineering and that was mostly "we know you're Korean but since you're here to work for Boeing we expect a basic remedial grasp of English out of our larger feeder schools."