Keith Johnstone: Impro
Nominally about improvisation theatre, but has many insights about human behavior you will not find anywhere else, especially about status hierarchies.
Maurice Nicoll: Psychological Commentaries On The Teaching Of Gurdjieff And Ouspensky, Parts 1-6
This book is probably the best introduction to the teachings of Gurdjieff that have quite literally changed my life. Gurdjieff was a spiritual teacher whose approach is quite different from organized religions, new age gurus and such.
This approach is for people who have experienced or have a sense that there is something that the materialistic world view cannot explain, but feel that existing religions are lacking, for example they require you to believe in things that do not make sense.
In this approach there is no need to believe anything. You become convinced by your own experiences about some fundamental truths about human organization and capabilities, allowing you to start learning more.
You could say that it is "preparatory work", allowing you to learn enough to be able to discern helpful teachings from those that are less helpful.
The book is out of print. To get a physical copy you need to order it used from Amazon. Usually they are sold one book at a time. Just get any one book, there is no need to buy the full set. The books record individual discussions, and the same topics repeat in all the books. If the book resonates, I recommend that you continue with In Search of Miraculous by Ouspensky.