This is my tried and true, detailed system for creating powerful scripts:
1. Brainstorm themes, plots, characters, settings, and major beats of the story
2. Organize the 3-5 plots into a beat sheet, giving each a beginning, middle, and end
3. Write a 8-10 page treatment (summary) of the story, including plot, character arcs, themes, etc.
4. Write a 1st draft of the script.
5. Let the script alone for a week.
6. Revisit the 1st draft, edit, proof, revise as necessary.
7. Create PDF and deliver final draft.