Choose the subject of your screenplay. It should be an interesting person whose life details will hold the interest of viewers. This person can either be deceased or still living. Written permission of the subject or the subject's family is highly recommended to prevent the chance of conflict or lawsuits.
Establish which parts of the subject's life the script will cover because naturally every detail cannot be included in a movie that is approximately two hours long.
Research everything about the subject and get a feel for his personality, hobbies, accomplishments and faults. He would need to be portrayed as a real, believable person with an interesting, exciting life.
Interview the main character along with his friends, co-workers, business associates and family. If he is deceased, his obituary would be the best source for a short summary of his accomplishments. The more dimension added to a screenplay, the more interesting it will be to moviegoers.
Use a script software to lay out the screenplay in proper format. It is possible to write without software, but it is extremely time consuming to set all the correct margins and spacing. There are several excellent programs on the market and even free software available online.
Look for software that has extra capabilities such as storyboards, index cards, and script notes and can be easily updated with new features in the future.
Write an outline of the script and begin the first draft. Each page averages approximately one minute of film, so you will need to write between 90 and 120 pages to complete a feature-length screenplay.
Most screenplays follow three-act structures with peaks and valleys of action. Strong, believable dialogue and action from your main character is essential to give him a distinct personality to which a movie audience could relate.
Review the first draft and check for grammar errors, continuity, and correct format. If the story is weak, additional research and interviews may be needed and the story line may even completely change.
Finalize the screenplay with a read-through with actors or friends, as this can be extremely helpful in pinpointing areas where additional changes are needed.
Use the feedback to make your final revisions.