Start here, then work backwards to Save The Cat & The Writers Journey & Aristotle.
Read plenty of similar scripts & watch plenty of movies.
Understand the difference between acts, sequences, scenes & beats.
Understand how a combination of character & plot creates STORY.
Understand what characters’ wants & needs are & how they drive plot to impact story.
Understand what your controlling idea or theme is—the most important part of all of this—then loop right back to the top of this post & start all over until it all becomes clearer.
Repeat as needed.