Since I believe it is a good thing to have lots of arrows in one's quiver, whether that be poker or some other venture, I note the following to you.
Myamoto Musashi - A Book of Five Rings
This small and short book is useful to a player of poker. Myamoto explains the stance and mental state of a samurai warrior - a mental state that works well when one is up to ones middle in a swamp infested with crocodiles all of which are intent on taking your chips.
Poker can be played at so many levels (beginners play any two cards relying on the chance element an aweful lot; more experienced players study the game and, I believe, get a lot more from poker because of all the intricacies that can come into play on every hand; professionals obtain sponsorship etc etc).
A Book of Five Rings can be read on many levels. The more one reads and understands the more one can read and understand at a new depth.
I mention this book because it is freely available online to both read and, if one, wishes to purchase. It is the teachings of a 17th century Samurai Warrior (potentially the greatest that ever lived) who put his life's thoughts to parchment shortly before his death.
To read the free online version go to http://samuraiconsulting.ca/5rings/
To purchase, pop over to Amazon or similar online book sellers.