In any given year a professor reads a lot of student writing. This year I have found myself referring students to two pieces that, if followed, would help my students improve their writing immensely. They are classics. I have read a lot of things about writing, some useful, some very mediocre. These two, while a bit dated and perhaps difficult for students to follow at times, are well worth it. And, like many old books and articles, they are available online!
Orwell suggests that unclear language, the passive voice, dead metaphors, are actually used to obscure meanings when the real message isn't very nice. I don't think that students pick up these habits from an intention to obscure meanings though. They just pick them up from whatever they are reading, from what they are taught, and from trying to write oral english, which is different from written english.
I have recommended these two pieces twice this week, so I thought I would put the two links together here - that way I can refer students to this link.