Source: https://www.capital.edu/uploadedfiles/content/academics/services_and_programs/career_development/personal statement guide.pdf?n=6524
Start by writing about an experience that initially got you interested in the field you are pursuing. Did your interest begin in high school? Or maybe you changed your mind during college; in this case you could begin by writing about the major you started with.
Continue writing about the experiences and activities (typically during college) that have reinforced that initial interest (making sure that your stories about these internships, work experiences, and research projects reflect your continued desire to pursue this area in graduate study).
Write about your long-term interests and how this degree program will prepare you for those interests. If you are beginning your statement using a specific event (likely from your years in college), you can continue by describing how you first became interested/engaged in this field, and then discuss your career-related activities and how they have affected your career path.