Here’s one quick way to define your story. Every hero must change so focus on defining what those changes might be and how to get your hero from point A to point B.
Every hero changes through the journey. If you look at bad sequels, they suck because the hero doesn’t change and just acts the same way they did at the end of the first movie. What makes the original movie good and most sequels bad is that the original movie has the hero change while the sequel usually doesn’t.
Consider a story divided into four parts: Act I, Act IIa, Act IIb, and Act III. In Act I, the hero is stuck in a dead-end life and needs to change, but doesn’t know how.
In Act IIa, he villain somehow gives the hero that chance and the hero reaches a False Victory. The main criteria for this False Victory is that the hero is mainly concerned with his own selfish goals. In “Die Hard,” Bruce Willis reaches his False Victory when he finally contacts the police about the terrorists. He’s achieved a goal, but this False Victory almost always helps only the hero, but rarely anyone else.
Act IIb, the hero realizes the error of his ways and in Act III, he learns something that causes him to take action with a renewed sense of purpose. In these final two Acts, the hero is no longer pursuing a selfish goal, but a selfless one. In Acts IIb and III, other people are in trouble and the hero has to act to save them.
Dividing a story into two parts, we get the first half where the hero acts Selfishly and the second half where the hero acts Selflessly.
By keeping that minor change in your story, you can help create a much larger character change in your hero. The purpose of your story isn’t for the hero to achieve his goal, but to achieve some sort of revelation about his own life that makes the hero a better person as a result.
The hero must see the error of his old ways that led to the False Victory, and then adapt a new way of living that helps him achieve the final victory over the villain.
The basic hero change goes from Selfish to Selfless. The details, of course, are left up to your particular story.