Every story is about change. Change implies contrast so every story is about constant change. Stories drag when nothing changes, so to avoid telling a dull story, make sure your hero’s life change constantly.
The greatest contrast is between positive and negative. That means one moment your hero’s life is going great and the next moment, everything seems to fall apart. Just when everything looks bleak, the hero takes action and makes life better again, only to have something happen to make it fall apart once more.
In “Avatar,” the hero has just made love to his alien girlfriend (positive). Suddenly the next morning, he hears the rumbling of bulldozers plowing down the forest (negative). He attacks the bulldozers (positive) but the Marines later identify him from video cameras on the bulldozer (negative).
In “E.T.,” E.T. is exploring the forest (positive) when suddenly humans appear, forcing the spaceship to take off without E.T. (negative). As the humans fan out, E.T. manages to evade them and escape (positive).
In “Frozen,” the hero and her sister are playing in the ballroom where the sister makes snow (positive). The sister accidentally hits the hero with a blast of cold, nearly killing her (negative). The parents take the hero to a troll who heals her (positive) but to avoid hurting her again, her sister isolates herself from the hero (negative).
This constant shift from positive to negative back to positive and negative again keeps a story from feeling flat and dull. Without such contrast, nothing will seem to happen.
Once you understand that stories must constantly change from positive to negative and back to positive again, you can sketch out the rough outline of your story by defining the beginning and the end.
In the beginning, your hero is in a negative situation. By the end, your hero winds up in a positive situation. On the other hand, your villain starts in a positive situation and ends up in an negative situation.
(In tragedies, it’s the other way around where the hero starts off in a positive situation and ends up in a negative situation. In “The Godfather,” the hero starts off trying to avoid the family business. By the end, he’s become the new godfather.)
In “The Hunger Games,” the hero starts off in a negative situation by living in poverty and worrying about her little sister. On the other hand, the villain (even though he’s not seen until much later) starts off in a positive situation by being completely in control of the Hunger Games lottery to pick tributes to fight and die in the arena.
By the end of “The Hunger Games,” the hero is in a positive situation, having survived, kept Peeta alive, and humiliated the villain. Meanwhile, the villain winds up in a negative situation as he now looks weak by not having a single winner of the Hunger Games.
In “Star Wars,” the hero starts off in a negative situation by living on a farm on a boring planet. On the other hand, the villain starts off in a positive situation by capturing Princess Leia.
By the end of “Star Wars,” the hero is in a positive situation by getting a medal for destroying the Death Star. Meanwhile, the villain winds up in a negative situation, having failed to destroy the rebel base.
Look at the beginning of any movie to see how the state of the hero is always opposite of the villain. If the hero starts in a negative state, then the villain starts in a positive state. When the hero ends in a positive state, the villain ends in a negative state.
In “The Martian,” the hero starts in a negative state (being stranded on Mars) but ends in a positive state (being rescued from Mars).
In “Harold and Maude,” the hero starts in a negative state (being depressed and suicidal) but ends in a positive state (embracing life).
In “Frozen,” the hero starts in a negative state (being isolated from her sister and being lonely) but ends in a positive state (being friends with her sister once more and finding love).
In “Django: Unchained,” the hero starts in a negative state (being a slave and separated from his wife) but ends in a positive state (being free and together with his wife).
Before writing anything, plot out your hero’s main change from negative to positive (or positive to negative if you’re writing a tragedy). Just this simple step will give your story direction and focus, which will make writing the screenplay much easier.