Read and study famous ancient Greek tragedies to better understand how authors wrote their masterpieces. Read commentaries on the plays to determine what made them so likable and how the playwright executed his vision.
Familiarize yourself with the structure of the Greek tragedies, then write out an outline for your own structure. Greek tragedies had prologues, Parados, which were songs and dances; episodes, during which characters interact and the chorus speaks; stasimons, which comes in between episodes and during which the actors leave and the chorus sings and dances; and the exodos, which comes at the very end, during which the chorus sings a processional number and leaves the stage.
Develop the character of your play. In Greek tragedies, there are usually tragic heroes who fail miserably at what they attempt to do, often losing loved ones and possessions in the process; there are also usually villains, wise advisers and lovers. Though the hero does not necessarily need to die at the end, they should have a tragic flaw which ultimately leads to some sort of downfall.
Write the music and choreograph the dances for the choral numbers in your Greek tragedy. Several parts of the play will require singing and dancing by the chorus. The musical numbers should clarify happenings and events in the play and are usually directed at the audience, as if the chorus was having a conversation with the audience apart form the actors.
Write out the dialogue and scene directions for your play by listing the name of the character, a colon and the words that they must say. Scene directions come after the colon as well, but have parentheses around them and are sometimes written in italics to differentiate them from dialogue.