Find an agent. Consult publications like the Writers Market or your local theatrical services company for an up to date list of agents that market stage plays. Some literary agents that handle TV and movie scripts also handle play scripts.
Research theaters and producers. After you write your play script, study the local theater directory and past issues of Playbill to determine which theater groups produce scripts similar to yours. Then set up an appointment with the theater's director or representative to pitch your script.
Produce the play yourself. If you're in a small town or a city without a structured theatrical community, put on the play yourself. Of course you'll need to recruit actors, set designers and stagehands, but if you advertise in the local alternative or college paper, you'll have no trouble finding qualified people. Find a space to rent in an artsy or trendy part of town, and start rehearsals.
Approach an actor or actress you admire. If a local (or even a national performer) fits one of the characters in your play, send an introductory email or letter to them or their agent. Sometimes the personal approach works best. If the actor likes your script, they'll have enough pull to get it produced-or at least read by an agent who might market the script for you.
Contact your local college, high school or youth group. If your original play script caters to a younger crowd, go to the theater director at the closet university or high school. Schools produce a number of plays each year and performing original material will give them prestige.