Brook, Peter. Evoking (and Forgetting) Shakespeare. New York: Theatre Communications Group, 2003.
This brief volume has considerable profundity. It consists of a lecture Peter Brook gave in Berlin in 1998 and (if I'm reading it right) a second, shorter speech he gave in Paris in 1994.
It's the second that particularly interested me. It gives a general overview of acting principles during Brook's long life in the theatre and his advice for portraying Shakespeare characters.