Zincy
In Vino Veritas
Writing a screenplay requires a level of understanding of writing, character design, cinematography, direction, and of course good editing. Or, access to people with those specializations.
The best way to improve a screenplay is to write one with those factors in mind. Create compelling dialogue, understand where your actors/characters will be and what they will be doing, the set up of the scene, the flow of action, and the timing.