Read professionally written television screenplays. According to Jane Espenson, writer/producer of shows such as “Battlestar Galactica” and “Buffy the Vampire Slayer,” reading actual scripts, rather than merely watching episodes, will help you learn the voices of the characters and the structure of television storytelling.
Brainstorm ideas for your screenplay. Each episode of a show tells multiple stories. The “A” story is the one in which your main character is involved, and the problem he encounters will require the entire episode to solve. The “B” story is regularly used to give supporting characters their own problems to overcome but are not as important to the show overall. A “C” story also can be developed if your show has numerous characters and they don't take part in the A or B stories.
Write an outline of your episode. Before you add the dialogue and action, sketch out each scene of your screenplay. This outline will act as a road map during the writing process. Refer to the outline as you write the script to remind yourself of the purpose and direction of each scene.
Add the action and dialogue of your characters. The genre of your show is an important element to consider as you write. Comedies must be funny, dramas must be filled with conflict and action shows must be exciting. The audience has expectations, and it is your job as the writer to satisfy those expectations.
Solicit feedback on your script from friends or colleagues. Suggestions will help you improve your screenplay’s authenticity, especially in the case of a spec, the goal of which is to mimic the style, tone and voice of an already existing show.
Rewrite your screenplay. Your first draft will not be perfect.