Write down a list of questions you might ask your character in an interview. Questions like "Where were you born?" or "What are your parents like?" are good places to start.
Answer the basic questions as you think your character would. These basic questions, which might consist of physical traits or personal history, will form a foundation for your character outline.
Ask more specific questions, and write down the answers. You may find some surprising answers that teach you things you didn't know about your character. Some specific questions might be, "What is your greatest fear?" or "What is your least favorite aspect of your personality?" These questions dig deeper by looking at a character's hang-ups, neuroses, and insecurities, which may factor into decisions she makes.
Read your answers and sort them into categories. These can include categories like "Basic Biographical Information," "Physical Description and Dress" and "Thoughts and Beliefs." These categories will help you to organize your character outline.
Type up the outline, using your categories as section headings. Beneath the headings, list the answers to the questions you asked your character. For example, under "Physical Description," you might list, "Brown hair," "Green eyes" and "Six feet tall."
Review your outline to see if any more questions occur to you. If they do, try to answer them as your character so you can add this information to your outline.
Print out a copy and keep it handy as you are working on your story or book. You can refer to it to make sure details are consistent, or if your character has to make a decision and you want to check how she might act based on her past or beliefs.