Study the Narrative theories of at least 4 people who have researched and written about the subject.
A good place to start is the Russian Vladimir Propp;
He came to the conclusion that most narratives have 7 key characters that appear on a regular basis.
Here they are;
The Seven Character Types of Vladimir Propp
- The villain—struggles against the hero
- The donor—prepares the hero or gives the hero some magical object
- The (magical) helper—helps the hero in the quest
- The princess and her father—gives the task to the hero, identifies the false hero, marries the hero, often sought for during the narrative. Propp noted that functionally, the princess and the father can not be clearly distinguished
- The dispatcher—character who makes the lack known and sends the hero off.
- The hero or victim/seeker hero—reacts to the donor, weds the princess
- False hero—takes credit for the hero’s actions or tries to marry the princess.
Be mindful that not every narrative has all of these characters.
Also remember that Propp was looking at folk tales and not films - so just be careful what you say!