Many people cannot resist the temptation to tell as much as they can, but a longer piece of writing doesn’t always equal a better piece of writing. For whatever reason you are writing the autobiography, think of the person who is going to read it. Imagine you were an admission officer or the judge in the scholarship committee, and you have to choose from hundreds, if not thousands, of autobiographies. At some point you will hate people who prefer to write long admission essays and autobiographies. There’s also a good way to check whether your writing is interesting or not. Give it to one of your most impatient friends, who prefers short articles to books and long stories, and ask for their opinion.
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.