reading about writing

Merely reading fine writing does have the potential to train one's ability to write.  At least it helps form one's judgement about what constitutes fine writing.  

NPR comes through with recommendations of three books that go another step: they are ABOUT writing, more specifically about writing for ordinary readers.

LINK

Stephen King is quoted: "If you want to be a writer, you must do two things above all others: read a lot and write a lot."