The aim of such an essay is obvious: you need it to convince admissions officers to accept you into college. As a rule, there is a word limit specified in the instruction for applicants. Don’t confuse an autobiographical essay with your CV or resume! They have totally different structure and formatting. In addition, the essay is aimed at portraying you as a personality, not as a professional.
As is present in the biography of a person, your place and time of birth, your parents’ views, an overview of your personality, your likes and dislikes, and important events that shaped your life should always be included in your autobiography. This will give a mental picture of your life to the readers as a sort of backdrop to the main part of the story.
“Talking about the past can have a healing function, but what we find is that talk, literally, is cheap,” Dr Hunter says. “We speak words and they fly away before we’ve faced what it is they convey.  This is not the case with the written word.  Writers find themselves saying, ‘ I never really thought about it before’ or ‘ I never saw it this way until I started to write it’.
Stick to informal language, unless it’s absolutely necessary to use formal terms. Instead of “utilize” you can just put “use”. Focus on simple language, with one or two syllable words. The only time you should be using higher level language is if you are using scientific terms or describing a technical process. Even then, you should be writing for the average reader.
Develop a central theme, main idea or thesis that clearly explains the purpose behind your autobiography. For example, your theme might be about how you overcame obstacles to become a stronger person, or it might explain why a particular passion -- such as mountain climbing or rescuing animals -- is so important to you. Back your theme with details and background information about your life experiences. For example, you might explain that your dad is in the military, so you've had to learn how to adapt quickly to new schools and unfamiliar environments. Or, you might discuss what it was like growing up in a poor, single-parent home, but how your family was always willing to take in injured or stray pets.