Choose a genre. Decide whether you want to write a drama, comedy, musical, tragicomedy, experimental or absurdist performance, or children's play. Determine where your skills and interests are strongest as a writer, and pick one genre or combine two or three.
Define the goal(s) of your play. Perhaps you want to highlight a social problem such as racism or homophobia. Maybe you want to entertain people and make them laugh. Theater has the ability to teach, challenge people and give them a night they'll never forget. By jotting down your goals, you'll help focus your play and give yourself inspiration as you write.
Create your characters. Make a list of their unique qualities and characteristics. It's well-accepted wisdom that writers should write what they know. If you have a hard time developing a cast of characters, draw on people you know to flesh out your protagonists. For example, maybe your mother is stubborn but sweet and your brother is a recovering kleptomaniac and a neat freak. Combine qualities of people in your life to create distinctive characters.
Outline your plot. If you're writing a one-act play (typically 20 to 30 minutes in length), your outline can be fairly short. Full-length plays (usually 90 to 120 minutes) will require more detail. Create a plot that provides your characters with obstacles that prevent them from getting what they want. Make the challenges they face believable and surmountable---even if your characters are ultimately unable to surmount them.
Write your play. Center character names on the page and format them in capital letters. Write each character's lines of dialogue beneath his or her name. Include parentheses around stage directions. For example: "NIKKI, smiling sweetly, breaks the eggs into the pan." Count on one minute of stage time for each page you write.