I believe every actor should have a well-worn, dog-eared and notated copy of Konstantin Stanislavsky's 'An Actor Prepares' on their bookshelf. This will be a constant reference for you and, if over time, you should have read all of Stanislavsky's works as these provide all of the background to contemporary Acting. You can get your copy here: https://www.takealot.com/bloomsbury-revelations-an-actor-prepare/PLID26924865

Happy reading!