Turning the Mind Into an Ally
Written in a very friendly-encouraging manner for beginners and those of us having trouble with their practice.
This is the main book used by Shambhala for their beginner guided meditation classes, and with good reason. Sakyong Mipham has lived in the west for most of his life and relates many of the Buddhist teachings in an easy to understand conversational style.
Chapter 11 covers the 9 Stages of Training the Mind. This is a very easy to understand explanation of the signs of how our practice is progressing.