Write a character sketch that includes your character's physical and personality traits. Create a back story for your character that gives him a full life. You can work in a notebook to create your character or keep notes in your word processor. The important thing is to develop your character fully. You can't sell a network on your character if you don't know who your character is and what makes him tick.
Develop a TV series outline. You need a vehicle for your character. The TV series idea is the next logical step. The show you create should grow from your character. The show will be the arena in which your TV character comes to life. Write a treatment, between five and 20 pages, depending upon how much of your series idea you've thought out. Include a brief synopsis of the series that explains the basic premise of the show. Think about your character's personality as you write. Determine whether the show will be dramatic or a comedy. Think about the situations you'll put your character in. The treatment should cover enough material to allow you to work up several episodes once you begin writing a script.
Write at lease one episode of your TV show. The pilot episode is what you will focus on. Use screenwriting software and a TV template so the software will format the script automatically as you write. The pilot episode should introduce your character and immediately put him in a dramatic or comedic situation. If your character has a complex back story, such as a character for a drama might, you will have to distribute that back story over the course of several episodes. Your goal now is simply to create a character, and building a TV series vehicle around your character, as well as at least a starter script, is important to fully realizing the character you've created.