When I studied in a Canadian University, our department had
a mailbox for every faculty member and graduate student.
Like security deposits in a bank vault, the boxes were arrayed
on a wall, with their golden faces looking out on a hallway.

I used to print out and drop off the draft of a paper I was
working on in my professor's mailbox. He would usually pick
it up the same day or the next. Within a week or two, the
pages would be returned to my box with hand-written
corrections and suggestions. I would go back and fix the
article in Latex (a document preparation system), print it
out, mail the improved version back to him, and the second
cycle began. This would go on, for months sometimes, until
he was satisfied for the moment. That, aside from weekly
meetings, was how we communicated and how I was trained
to express ideas clearly and correctly on paper.

Understandably, I made many basic mistakes early on, e.g.,
using "it's" for "its," wrong English article usage, etc.,
which took a long time to get over with. For form, he didn't
like a single word taking a whole line at the end of a paragraph.
So I acquired that taste, too. Those days, I just felt ashamed 
to be caught repeatedly with rudimentary errors and
impressed by his saintly patience as he pointed out them
each round without ever telling me in the face that I needed
to improve. He kept praising my writing and at the same time
never failed to point out my mistakes. That was his style, 
easy to admire but hard for me to immitate. Nonetheless, 
after four years, I was able to produce papers that sometimes
induced comments like "very well-written" from reviewers.

I don't remember he recommended any books on the topic. But
as a computer science major, I read Brian Kernighan and from
there discovered "The Elements of Style" by Strunk and White
(which I recently gifted to my nephew H on Christmas). A few
rules from that book stuck, e.g., "Omit needless words!"

I knew enough that writing was an important skill to thank
my professor for it in my thesis. But little did I know that 16
years later, I would enjoy the craft as a daily practice.
Hallelujah!