The basic spine of any successful screenplay comes down to four key elements: character, objective, obstacles, and theme.
A good story is about an interesting protagonist (character) who wants something badly (objective), faces resistance in achieving it (obstacles), and illustrates a universal message worth telling (theme).
Since stories have been recycled and reinvented for centuries, understanding common archetypes can help you identify what kind of narrative you’re building. Classic plot archetypes include the quest (Lord of the Rings), rags to riches (Annie), and beating the monster (Jaws). Story archetypes are equally familiar — none more so than Good vs. Evil (Star Wars), where the forces of good triumph despite overwhelming odds.
But plot and story archetypes are hollow without theme. Man vs. Nature (The Perfect Storm). Man vs. Society (V for Vendetta). Man vs. Self (The Verdict).
Theme is what gives your story its reason to exist. When you think about theme clearly, it forces the essential questions: Why must I tell this story? What am I trying to say? What is it really about? These are the most important questions a screenwriter can ask — and answering them honestly is what separates a story worth telling from one that merely fills pages.