As writers, we all know the characters in our story are as important as is the plot. You need to make your characters believable, and interesting to make the readers care about them and what happens to them. You need to know u\your characters as well as you know yourself or a family member of significant other. When thinking about a new story, you should write up backgrounds and dossiers about the characters involved; both the protagonists, antagonists, and all the other major characters that appear in your work. Make a separate file for each one.
Don’t hold back when doing these backgrounds. You want your characters to be living, breathing people, not some cartoon character. They have families, friends, jobs, hobbies, quirks, bad habits, and lives they lead. The story you place them in is an interruption in their life and knowing your characters well, will enable you to show how they grow and change over the course of the book. Knowing your characters will allow you to show how the characters change as the story progresses.