Film is, arguably, the dominant art of our time. It is also, usually, a narrative form. It makes sense, then, to study film if you are interested in narrative. Good films are often masterpieces of narrative structure and great films always are.
A good start–candycanesammy’s Thoughts on Film website, especially this post: WGA 101 BEST SCREENPLAY LIST RECAP, written on 13 January 2011. In this article, candycanesammy explains what he has learned from watching and analyzing the films on the WGA Best Screenplay list. His analysis is chuck full of nuggets of writerly goodness. Highly recommended for fictioneers.