Timothy Keller. Prayer: Experiencing Awe and Intimacy with God. New York: Dutton, 2014.
This is probably the best overall book on prayer that I know of because it shrewdly addresses the issue from three angles:
- experiential or devotional
- methodological or practical
It seems like every book Keller writes is the best all-around book on that subject.
This chart is particularly helpful (p. 141):
I agree with Andy Davis’s review.