Writing a script for a TV or shows needs ingenuity and creativity, it should be an interesting piece that will makes people yearn to watch the next episode so start by assembling your idea of the story
Chose the genre and develop the story to include the hero's or heroine or maybe have a better line for the main character and the supporting character.
Outline other characters in the series or movie and developed them in a very creative way. Write out the story fully and revisits it by going through it again.
Don't forget to let someone good in this area see it and give his or her input,it will help you have an external input that might give the script a better outlook.