Research the type of show you want to make. Since it is an animated show, watch animated shows that are popular in your area. Look for similarities in style, subject matter or genre. If you see many similar types of work (possibly by the same artist or writer even), it may signify a current trend. Ideally, you will be able to identify a trend that has not yet started; for example, when the Twilight books became popular they started a new vampire trend and inspired movies and TV shows.
Identify your concept and story. Maybe your story is about teenage vampires trying to become human. Since this is an animation, you should also have an idea of how it should look; for example, is it more anime grunge or a Simpsons-type look?
Create an elevator pitch. The idea behind the elevator pitch is that you should be able to communicate the entire story within a few seconds. This is where lines like "It's Jaws meets The Fockers" come from. The elevator pitch should be two or three sentences that communicate enough of the story, design and background to entice; for example: "It's Animaniacs meets Shiki: grundgy vampire slapstick comedy."
Write down an outline of your idea. Be specific when describing the storyline and characters. Use a lot of descriptions to "show" the reader your story and help them imagine it. You should also include suggestions for possible artists if you have any. This outline should ideally be two to four pages in length.
Register your creation with Creators Vault to prevent it from being stolen, then submit it to production companies and TV Writers Vault to try to sell it.