For any writer struggling to create powerful and believable characters, it is imperative that you understand the psychological aspects of why people do the things they do, why they behave in the ways they choose to, and what inner drives propel them towards potential greatness. The hero's journey talked about in myth and story has a structure based upon archetypes, themes and patters of human behavior that any writer can come to master when creating the perfect screenplay, and "Psychology For Screenwriters: Building Conflict in Your Script" by screenwriter and Assistant Professor of Psychology William Indick is a priceless guidebook for navigating the interior of the mind.
What works really well in this book are the many examples of how these aspects of personality show up in films most of us have seen before. This really allows the author to drive home his points and clarify his concepts in a way we call can understand - by relating it to what we've already experienced on the big screen. Even better are the many helpful sidebars, chapter summary points and insightful exercises all geared towards making sure that the writer, and reader, truly understands the material before closing the book and beginning to write.