The #7 Key Step:
Find a batch of 4 x 6 index cards and write each one of your characters at the top of the card. Next, think about the role each character plays in your story, and what kind of person each is: age, education, place of birth, appearance, mannerisms, personality.
Some characters will be major ones during the action of the story; others will play only bit parts. Regardless, the details of their personalities and lives are critical to adding interest to your story.
You must remember, however, that every character must have a reason for being. If they do not, they will slow the book down and worst of all, bore the reader.
Using this same index-card technique, Alfred Hitchcock would write down information about each scene of his film, one scene to a card. By the time he was ready to shoot, he had a completely developed story -and a tight one at that.