Use a software program such as Final Draft or Celtix to help with formatting an industry standard screenplay layout; or set your margins and tab stops manually in your word processing document. Adjust your custom left margin to 1.5 inches and the right margin to 1 inch. Pre-set your tab stops at 2.5 inches, 3.7 inches and 4.2 inches.
Type your script in 12 pt. Courier font, which is an industry standard.
Start your script with FADE IN at the top of the page aligned at the left-hand margin. End your script with FADE OUT two single lines below the last scene of the screenplay and align it on the right margin.
Write scene headings to start each scene. Type in upper case stating whether the scene is an interior or exterior location; include the name of the place itself and indicate the time of day. Write it like this for example -- EXT. EMPIRE STATE BUILDING -- NIGHT.
Write your scene directions in sentence case from the left margin, single-line spaced. Position the scene directions two single lines below the scene heading. Write different scene actions as separate paragraphs with two single lines between the paragraphs.
Type character names in upper case and provide brief notes about the age and physical characteristics the first time they enter the script. Type any sound described in upper case. Keep it brief and to the point and don't write narrative descriptions.
Position your character name near the center of the page, two single lines below the scene direction. Press the "Tab" key three times to take the cursor to near center, if you are using a word processing document.
Position any parentheticals on the next line and press the "Tab" key twice to take you to the typing point. Write only brief actions here in parentheses such as (on his cell phone), (reads) or (to Anna) to make it clear what the character is doing while talking, or to whom he is speaking.
Write the dialogue on the next line and press the "Tab" key once. Write dialogue in sentence case and always single-line spaced. Note that a line of dialogue should be no longer than 3 inches in length.
Start your screenplay with an engaging hook so that the reader and viewer will want to keep watching. Tease the audience with something interesting happening.
Introduce your audience to the protagonist of the story almost immediately, followed by other essential characters. Allow your viewer to identify with the characters. Try to write naturalistic dialogue that serves the character and propels the story forward -- don't waffle with irrelevant detail.
Plot the moment of conflict which begins the story within the first 10 pages of the script. It is best not to introduce it immediately as you have to introduce the setting of the story first and you don't want the latecomer to miss the whole point of the story.
Plot a story which progresses to a climax. Write it as if you're peeling layers of an onion slowly and don't show too much to give your plot away too soon. Keep things back to be able to inject your story with unexpected surprises.
Rewrite your first draft as many times as it takes until you are satisfied that it is the standard of a professional screenplay. Don't avoid this step as the craft of writing is in the rewriting of it. Send the first draft of a screenplay to a producer and it is most likely to be rejected as poorly written and underdeveloped.