Save the Cat by Blake Snyder is the best book on screenwriting there is. He simplifies and demystifies what makes a script work. His "beats" technique is amazing and really helps in the writing process. Blake's information goes beyond the basics of formatting a script and how to write. It's about what sells a script. He covers the importance of the log line and how to create an amazing one, the ten genres of all films and the fifteen beats that occur in all films. I highly recommend this to any writer, amateur or professional, seeking to improve their writing as well as understand what makes other scripts good. It's an amazing book. Writing is much more fun now that I follow Blake's methods. He took the guesswork out and made a workbook that's easy and fun to follow along with on the journey of writing the next great film.