Write a step outline. The step outline is a scene-by-scene map for your screenplay to follow. Write each major event that happens to the characters in your screenplay's story, in sequential order. Give the story a distinct beginning, middle and end. Write the outline, which only you will ever likely see, on a writing pad, by hand, or on your computer.
Create scene cards for your story, using index cards. Write one scene on each index card, using a pen or felt tip marker. Arrange these cards, in the order that they happen, on the desk or floor in front of you, or thumb-tack them to the wall.
Rearrange the order of any scene cards, as you plot out the story in the most dramatic way.
Write the actual first draft, or rough draft, of your screenplay on your computer. Write the script in the proper industry format, using the step outline and index cards as guides.