Once you have the fundamentals down you should be reading books that are not poker books, but are related. A great example is "Bridges Out of Poverty," which provides outstanding insight into the minds of people from different classes, especially poor people. After reading this book felt it was easier to instantly classify people and get in get in their heads. Another very insightful book is "The Likeability Factor." Some classics include "The Prince," "The Art of War," & "The Five Rings."