The lessons for getting started are
quite standard. First, you need three
books or, now, Web sites, one for each of
a good English dictionary,
a good English grammar,
and a good book on rhetoric. For a
dictionary, sure, something by, say, Webster's.
For grammar, something used in senior English
in high school or freshman English in college.
For rhetoric, sure, Strunk and White, The
Elements of Style. Not nearly new stuff. For
more, The Chicago Manual of Style can
provide clear answers to some tricky questions,
good answers not easy to find elsewhere.

Then you iterate: (1) You write something,
a postcard, an e-mail, a birthday card,
a blog post, a love letter, an elevator pitch, a term paper, etc. Hopefully
you can get others to read what you wrote
and get some feedback or at least some reactions.
Then with what you
noticed yourself while writing and from the
feedback, you identify some issues or problems
in your writing. (2) You read, hopefully
well written material. Here maybe the best
is good material from the STEM fields
and good material from the world of literature.
In that reading, you try to see how that writing solved
the problems you noticed so far in your writing.
And you try to learn more. Then you return to (1)
and iterate again.

Then for the iterations of (1) and (2), devote
at least 10 years before you expect a lot of
improvement. Good writing skills are likely
the most difficult learning considered in
education, and I say that is a devoted STEM
student with high contempt for belle lettre.
As a college prof, I saw that the adult evening
students, while not very good as students, were
much better at writing than even the good
students of usual college age -- the extra
years of reading and writing, in a deliberate
effort to learn more or not, were the huge
difference. Net, the learning takes years --
call that decades.

For STEM writing, there are some special techniques.
Maybe the best, pure form of these techniques
and, thus, the easiest to place to learn is in the
best quality pure math and mathematical physics.
For pure math, sure, emphasize Halmos, Rudin,
Bourbaki, von Neumann, Breiman, Neveu,
authors of college texts on abstract algebra,
e.g., Herstein, etc. There are lots of
highly polished freshman calculus texts, and
can learn a lot about STEM field writing from
those examples. A good text on freshman
college physics also has some really good lessons
to teach on STEM field writing. Maybe you
want the math/physics and maybe not,
but there are good writing lessons there.
For writing in computer science, sure,
like it or not, Knuth's, The Art of
Computer Programming. Knuth's a good
writer on computing, e.g., just his
The TeXBook is some especially good
STEM field writing.

For literature, one of the main goals, whether
they say so or not, is art as in the
common definition of the communication,
interpretation of human experience, emotion.
To oversimplify, call such writing belle lettre.

With some irony, belle lettre commonly is really
good communicating the passion, pathos, poignancy,
plight, and pain, and other such awful alliteration, of the
human condition but otherwise nearly useless
at communicating something effective to
alleviate the pain, etc. Then the STEM fields
and its writing are less good at the emotional
communications but now in this the 21st century
often just astoundingly good at
getting really solid, safe, effective solutions
to the pains. Which you prefer is your choice!

Or, in simple terms, do you want to
suffer with the pains or do something about them?
Yes, I know this remark is judgmental,
provocative, potentially pejorative, and other
such awful alliteration. Here people can
agree to disagree, and YMMV.

I'm no good at writing, but the above is the
best I know about learning how to do it. And
a lot that I'm saying is quite standard --
not nearly new, for more awful alliteration.

Go for it. And, here on HN, show us what you're
getting and what you've got! When you've got
lessons for other learners, show us those, too!

Good news: There are a lot of people who
are plenty bright enough to write really well
but are nowhere nearly bright enough to
have anything worth saying! Lesson: Don't have
to be very bright to write well! Or, if you
are bright enough to have something to say,
then nearly necessarily you are more than bright
enough to be able to learn to say it well!