CHOOSING A THEME
There must be a universal theme, or truth, that the audience can plug into. Know what subject you are exploring and pursue it in terms of a grand argument.
ORGANIZE THE PLOT
Write out your main plot points in terms of the main character deciding on courses of action to illustrate the theme.
Reveal just enough information about the locale, character backgrounds and relationships so your audience understands the framework of your story. You can withhold various pieces of information to generate intrigue, mystery, suspense and anticipation.
Ensure you have covered the key plot points; act breaks, inciting incident, midpoint, climax and conclusion. Even in non-linear stories, they exist. Tailor their moments of appearing in your story. If the first act of your stories doesn’t warrant 30 pages, so be it. Take what you need to service your story.
Many stories have a secondary plot which must intersect with the main plot to add bulk to your story. Often this is a love story.
Make your characters sparkle. Add dimension to their behavior. In a cluster of standardized behaviors for their personality type, add an outlying characteristic (such as compassion in a mass murderer) or a quirk to make them more interesting. Give them escalating conflict and moral dilemmas.
Audiences fall in love with characters but remember snappy dialogue. What will end up as catchphrase or being referenced in other films?