In the long, long ago, when I was an English instructor, I had perforce to use university supplied rhetorics, as they were called, and as I became dissatisfied with each one I used, I began searching for one that didn't give bad or useless advice. Telling my students of the various faults of the book they had had to buy did not go over well, but I could hardly let them read advice that would steer them wrong. I never found that book, but a colleague of mine did, and recommendation that I give it a look changed my life.
This was it, the one perfectly safe, perfectly reliable book about writing I have ever seen--and it's not even a book, as you can see from the title, about how to write. It is about how to read, however, and reading is the one necessary activity for learning how to write, so it works out well. If you're interested in how prose really works, if you want to see how much fun rhetorical analysis can be, then this book is it.
One caveat: the extent to which you reject (or even simply don't understand, at first) the things Lanham is saying in this book is a good measure of how useful this book can be for you. I remember struggling with much of it at first, myself--and I was already almost halfway along the path to enlightenment. As it were.