Favorite subjects, pastime, friends: here you transition to the place where we assume you are currently, so be careful and don’t say something offensive about it if you write a school essay.
Write about things that shape you, not about just some casual issues.
Early memories: shy or extrovert, always in the midst of fun or maybe a lonely child; cool events, long-dreamed presents (like a bike or an inflatable pool). Maybe you started reading early or found writing easy, or loved swimming, or sang with dad from the age of two.
How you went to preschool, how you transitioned to school, which school you attend.
Early childhood: your name, when and where you were born, names of family members.
Include some interesting points about time or place (snowy, beautiful, typically American, foreign country, interesting professions of parents).
Be sure to speak about sports, clubs, social activities, volunteering – everything that you do after classes and what makes you an active citizen, not a lazy person. They show you as a well-rounded person, active and cool.
Mention some sport, maybe art, or volunteering for some socially meaningful cause.
Use a voice in the autobiography that reflects your personality.
Don't use slang or write too casually, but avoid stuffy or academic-style writing that drains all of your personality from the piece.