Before rehearsal, the play's outline, structure and rate of progress are carefully mapped out, and the roles and mood of the scene are determined. Then the actors are allowed to express themselves spontaneously. The sparks given off in improvisation may have a major effect on the original plan, which may be expanded or cut down accordingly.
這其中有一個吊詭：排演前戲劇大綱、結構圖及進度表全部精確排好，角色和情境也都設定後，再來給演員即興發揮；而即興激盪出來的火花又可能大大影響原先的設計，而有大幅增減。