Begin this task early. Because the autobiography is one of the most important parts of your application, start early enough to avoid feeling rushed. This also will allow time for multiple revisions, if needed.
Review the university's requirements for your autobiography, which may include certain topics or a limit on word count. To ensure you've followed all the guidelines, list the requirements and plan your essay with these in mind.
Write an outline. Each section of the essay should say something significant about who you are. For example, move from birth circumstances to school years, to college and work experience or master's program (if any), and finally to future plans and why you want to enter a doctoral program.
Write your essay, using the ideas and points from the outline. Your writing should demonstrate your ability to properly use the three Cs: conciseness, clarity and coherency.
Revise your essay. Read it in a critical manner, looking for flaws or portions that violate the three Cs. If anything need revising, return to your draft and correct it.
Repeat the revision process until you find nothing more to amend.