One aspect of studying Japanese that has greatly frustrated me is my university's lack of writing classes. Learning kanji, vocab, grammar and an academic or other style is important, but Japanese rhetoric at its core is also structured differently than that of English.
For example, I remember learning how to write an essay in English for the first time. The teacher showed us that formula everyone knows: introductory paragraph with a thesis, supporting paragraphs, and a conclusion that restates the thesis.
Formulaic writing like this gets old, of course, but the basic idea is adhered to pretty well in English writing. State your thesis and support it. The first time I read an essay in Japanese, it was from some 社会学 study thing from a 東大 professor. It was designed to help Japanese students pass entrance exams. It was useful in some ways, but it was also very frustrating. I was frustrated because the author would say things like "I hope you found the thesis. It was right there, in that third paragraph. There's something wrong if you couldn't find it." I'd reread the passage over and over again but it was always difficult for me to understand the structure of the writing. "Of course I couldn't find it. Why is it in the third paragraph?!"
A Japanese person told me once that they structure their rhetoric opposite ours, saying that we put the thesis first and they put the thesis last. I think that is probably an oversimplification. My wife has been doing some interesting cultural studies and has led me to field of contrastive rhetoric; this article for example looks like a promising help to understanding. All three of the listed Japanese rhetorical structures would be very difficult for an English reader to understand.
I want to know some good resources to polish my writing skills in Japanese. It would be nice if there were something in English, similar to this Korean textbook, simply because it would be able to highlight the contrastive structure between English/Japanese writing styles. But something in Japanese is great, too (I remember seeing writing books at The Daiso, but something else would be nice). Perhaps there is a popular kokugo textbook for college/high school students?