Choose a topic, day, lesson or achievement that will be the theme of your essay. Consider that the admission essay probably has a word limit, which won't give you time to cover your entire life story. Plan to tell about a particular anecdote which reveals who you are. Spend some time brainstorming before you make your selection. You should focus on your strengths and abilities that set you apart from others.
Make an outline detailing the flow of your essay. It should have a clearly defined beginning, middle and ending. Since the person who reads your work will probably have several others to read, consider how you can grab the reader's attention immediately. Like any good story, you want to reel the reader in.
Fill in the outline with descriptive details. Shed light on things you remember distinctly including your own feelings. Keep in mind that the reader has not met you before, so share as much as you feel is necessary for the reader to have an idea of the type of person you are.
Write out a draft of the essay and remember to sell yourself. The autobiographical essay is a chance to talk about the things you've faced and achieved. Find a balance between persuading the reader and letting them in on your life. The conclusion of the essay is a great place to state what your autobiography means and explain clearly why you deserve admission.
Proofread the essay at least twice before giving it to others for feedback. After proofreading it a couple times, it might help to walk away from it for a couple days or a week. Then return to it with fresh eyes and look for places where it can be improved. Submit it only when you are satisfied with a polished final piece.