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.
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.
Incorporate dialogue into your autobiography to make it more personal, recommends history professor Robert Gerlich at Loyola University in New Orleans. Consider including humor when it's appropriate. For example, if you're writing about how you got lost at Disneyland when you were 10 years old and how the experience helped you learn to face obstacles, problem solve and overcome your fears, you might write, "The attendant at Splash Mountain said, 'Are you OK? Did you get separated from your family?' I quickly replied with as much bravado as I could muster, 'Nah, I'm fine. My eyes are just wet from the ride.' I didn't want her to know I was crying."