Go for teachers rather than books. The whole point of the Alexander Technique is to learn to feel instinctively when you're doing something right and this isn't aided by looking in a mirror. This thread has spurred me to find a teacher again. Did some lessons years ago and found I could hit notes with a power and range way beyond my previous abilities ... and then over the years the old bad habits have slipped back.

PS The only thing is, it takes over your life for a while. You catch yourself driving absent-mindedly while you concentrate on correct alignment while holding the steering wheel!