A stage play is written with the author or playwright deciding what each character will say in given situations. There are two main ways of representing this; the first is to write the character's name in the center of the page and then his dialogue directly beneath beginning at the left margin. This has the advantage of making it clear whose line is next and allows for easy following of the play during rehearsal.
However, the more common form in playwriting is with the character's name at the left, and then his dialogue aligned with the TAB to the right. This is there is less waste of space on the page and more dialogue can be fitted. As well as the dialogue, the playwright may put in various directions in italics or parentheses. These directions can deal with emotions and movements representing the meaning of the play. Stage directions should be kept to a minimum, however, as generally in a published play, stage directions in italics are those of the first director of that play.
Writing a screen play differs once again from a stage play. Writers of screen plays have infinitely more freedom to incorporate the sights and sounds of nature in their writing. Screen play writers on the one hand are free to take their play outdoors or to exotic settings, but meanings and nuances will be more subtle. For instance, a film scene might have a camera panning across a filthy street as a mute statement of the lack of sanitation services.
The screen play writer may also include directions to actors and directors as to how they believe each role and scene should be played, but, in the end, unless the playwright is actually directing the production, directors will do as they see fit and actors will interpret their characters.
The screen play should be set out in a similar way as the stage play except that the writer needs to make clear distinctions between scenes. Writing each scene in its own mini screen play packet will clarify any confusion. A clear knowledge of directing techniques is a distinct advantage as, when turning a novel into a screen play, you can arrange scenes in the order that a director will film them to expedite production.
A popular form of playwriting in the early 20th century was the radio play. In this genre, the audience is asked to imagine the action as they listen to the dialogue and the tell-tale sounds of the actions in the plays. A radio play writer also has more freedom in settings than the playwright does, as scene changes can simply be done by adding a narrator to describe changes or writing the changes of scene into the dialogue. Play writing should be set out in a similar way as the stage plays with several significant differences. Character names should be set at the left margin and preferably in capital letters to avoid confusion with the dialogue. Whenever there is a sound in the play, it should be scripted just like a character would be, but instead of the character name, the letters FX are written. In this way, the producer knows that an effect is to be inserted.
A good idea for radio plays, especially comedies is to double-space between characters, as actors will often ad lib lines that a director may want to script into the play.
Finally, timing is important in a radio play. A typed sheet of A4 paper with single-spaced dialogue will usually last a minute, but ensure that you time the sequences and know how long the plays will take on air.