Create a plot outline and main character sketches. The writing process is different for each author, but most can benefit from some simple planning. The first few pages are not the place to develop your character. Instead, having a game plan for how your movie will progress should be evident from the beginning of your screenplay.
Demonstrate your strengths. If you are particularly strong at writing dialogue, this should be showcased in the work. In this case, keep the direction and setup limited and allow the interaction between the characters to shine. If your storytelling ability is what would drive the film, set the scene for the reader with information about the setting and some thoughtful direction.
Focus on the genre of the film. For example, if the screenplay is science fiction or fantasy, this should be introduced in the first few pages. This could be done with something as simple as "INT. SPACE SHIP ON THE PLANET VENUS" or a well-written paragraph that introduces the setting.
Show the character, do not tell about them. This is the same for all effective creative writing. For example, you wouldn't say "Dawn is pretty and very rich." Instead, you could place her in her mansion home where she is gazing at herself in the mirror. Trust the reader to infer from your context clues and direction.
Create a conflict. Your main characters should be briefly introduced within these pages, as long as some indication of their motivation and behavior. To grip the reader, introduce some sort of conflict that will keep them reading. The idea is to get them interested in the lives of the characters and what lays in store for them. The longer they read, the more invested they will become in your work and the more likely they will be to consider your screenplay.
Edit and revise carefully. Your screenplay should be completely free of errors. Errors would compromise the integrity of your screenplay and make you seem unprofessional. Keep the reader focused on the content, not the embarrassing spelling error or inappropriate word choice.