Write your story's synopsis. Decide what the overall plot of the entire storyline is. Try to get it into 1 paragraph, then down to a single sentence.
Decide if your story is for a movie or a television series. A movie would only involve 1 90-minute to 2-hour long story. A TV series can take several hundred 30-minute stories.
Design your characters' profiles. Create their backgrounds, strengths, weaknesses and values in as much detail as possible. Make their personalities as over the top as possible.
Create a first episode if your story is for television. You'll want to introduce your characters and introduce the bare minimum of the storyline. Make sure your audience is intrigued enough to continue watching.
Write the story and lay out the storyboard. Decide how many episodes the story will be if it is for television. Decide what plot twists will occur and when (placing them at 1 and 2/3 points is often best).
Find an anime artist who can bring your characters and story to life. This is not needed if you can draw yourself. Otherwise, art schools and anime conventions are good places to look.