A far, far better book is "The New Rules of Posture".  See my review at  which also briefly explains why "8 Steps" is bad.
But for anyone reading this comment, there are two things I want to share, from hard-won experience:
1) Back pain and posture are incredibly complex and counter-intuitive, and come from a complex interplay of biomechanics, perception, and emotion. Anyone who says "just sit up straighter" or "just strengthen your core" or "use a standing desk" or "stretch more" or "it's a muscle imbalance, go to the gym" or "do yoga" doesn't know anything. Even if you think one of these helped you, it depends on the individual and they can do even more harm than good depending on the person. I think there's even more popular quackery in posture and back pain than there is in nutrition, and that's saying a lot. Even most doctors don't have the slightest clue -- which should be self-evident, given how many people have back pain and how it's not getting fixed.
2) The best place to start is "The New Rules of Posture: How to Sit, Stand, and Move in the Modern World" by Mary Bond.  It's the only book I've come across that takes the right holistic approach, but still maintains respect for "hard" science, explains the theory (medically, not according to any "school") but also gives you guided exercises. Start there, and then once you've gained a decent understanding of your body, you'll be in a place where you can figure out what more specific techniques you need, if you do (e.g. whether Alexander technique or psychotherapy).