It is a theatre book, but not one specifically aimed at stage management- Backwards and Forwards: A Technical Manual for Reading Plays by David Ball was without a doubt the most useful, informative, eye-opening book I read in my 4 years of school. I cannot stress enough how much every theatre artist needs to read this book. It was assigned reading for the Fundamentals of Directing class I took as a senior, and after reading it, all of the students in the class told the professor that she needed to assign it as the first thing that all of the Intro to Theatre for Majors students have to read as freshman. We honestly couldn't believe that this book existed and nobody had told us to read it before our senior year...
It's written mainly for actors, directors, and designers- how to read & break down a script in all of the ways that you're taught in beginning acting classes, but the way it is explained is so much clearer, so much better explained than any other way I've ever read. I'm gushing now, so I'll stop, but I HIGHLY recommend it.