film marketing book
Working as a film publicist I've found the following book to be extremely helpful:
Marketing to Moviegoers: A Handbook of Strategies and Tactics, Second Edition
by Robert Marich
Also, if you have the time and cash, courses through UCLA Extension online or on-site are really good and helpful, providing you with tons of information you can take with you and use in your work. I recently took a short filmmaking and marketing course online and learned a lot -- I have dozens and dozens of pages I printed out with endless resources I'll probably be using for years.
Good luck!