I am using several screenwriting books to help develop and format my screenplay.
The book, The Hollywood Standard: The Complete and Authoritative Guide to Script Format and Style (Hollywood Standard: The Complete & Authoritative Guide) provides the script standard from the Warner Brothers studio. It has a helpful index and examples of proper formatting.
The book, Save The Cat! The Last Book on Screenwriting You'll Ever Need is an inspirational book offering encouragement to screenwriters. It lists the rough plot and character rules for a commercial Hollywood script. Save the cat refers to an early action of compassion by a character done to endear them to the audience. It allows the audience to see the soft side of character and allow them to care about what happens to this person.
The book, The Screenwriter's Bible: A Complete Guide to Writing, Formatting, and Selling Your Script provides additional information on script development and offers ideas on selling your script.
Of the three books, Blake Snyder's was the most entertaining. For day to day referral, the Hollywood Standard has been very useful for sorting out issues related proper format.
Let me know if you have found others to be helpful.
