The overall application package will represent who "you" are to people whom you will most likely not know personally. The written expression of your qualities as an applicant will often be a very important way for committee members to get to know why you are an acceptable candidate for their program. Thus, it is essential to take great care in preparing this part of your application. Because graduate schools make important selection decisions that are partly based on what you say in this essay, the writing of it can be an intimidating prospect.
Write the first draft from this, then try to find an angle or a hook which can sink into the admissions committee; a good place to start is with an original and provoking opening paragraph. One of the worst things you can do with your personal statement is to bore the admissions committee, yet that is exactly what most applicants do. Admissions committees see thousands of "I have always wanted to be a." opening paragraphs, so a good way to make the essay more interesting is to write about an anecdote or memorable incident that led you to choose the particular profession. This can help add drama, vitality, and originality to the statement. It is important, however, that the anecdote is related to the questions asked and not just a retelling of a catchy life drama.