Communicate who you are and your interest in the field through stories and examples.
Why are you interested in this field? Is there a specific event in your studies or in your personal life that sparked your interest?
Why are you qualified? What courses, internships, jobs, or other experiences prove that you have the skills needed for this field?
Why this graduate school? Mention professors or aspects of the program that appeal to you.
What are your future career goals? Link the program specifics to your goals.
Some applications call for a 1-2 page statement, while others require responses to a series of questions. Schools will usually want to know some variation of the questions above. Do not write one statement and submit it to everyone.