Consider why anyone should read your story. Create an outline of your life and find the "spine" of your story. This will essentially become the theme and main reason for people to read. For example, you might be a poker champion, have six college degrees or have raised eight children. Find the purpose of your story and everything else will branch off from there.
Often, a person's childhood informs their decisions and life into adulthood. You should include your childhood whether it's a separate chapter or infused through flashbacks throughout your biography. Key things from your childhood include your home, friends, neighborhoods and different life experiences that may not be common to others, such as unique holidays or traditions.
Your family life is a branch of childhood. A family often defines a person and can explain a lot about their choices and lifestyle. Even if you had no family, the impact of that will be a huge part of the biography. You do not need a detailed family tree, but rather use personal stories to reflect family life, like the "Infamous Thanksgiving of 1998."
Include any major life events that have occurred. This branches off from the spine of your story and should include several stories related to that event. For example, a car crash, winning the lottery, losing a family member early on, surviving an attack and things like that make for dramatic writing and can further show off your personality traits like bravery, thoughtfulness or humor.
Use many back stories to depict your life instead of simply telling about your life. For example, do not state you are a bad cook; tell a humorous story of how you tried to bake cookies with the kids and they came out burnt. Stories can be used to incorporate multiple layers such as humor, skills, family time and the everyday traditions in the home. If you are writing a survivor's tale, use as many "showing" details as possible. For example, if you were hanging off a cliff and scared for your life, show how you were scared. Describe the sweat on your forehead, the shaky fingers and chattering jaw.