Discuss why you're choosing a certain career. For instance, If you plan to major in public health, talk about how you lost a few relatives to breast cancer. Include how their deaths inspired you to help others be knowledgeable about early detection and treatment of preventive illnesses. This includes personal involvement in counseling patients and community activism.
Show how the school will contribute to your long-term goals. You can do this by researching the school you're interested in. If you want to attend Howard University, for instance, talk about its longtime commitment to assisting minorities in receiving a quality education. Its goal is to help them prepare to serve their communities with the skills they would learn. You could also discuss how you're pleased with the school's emphasis on community service as evidenced by their many outreach initiatives.
Mention significant achievements. For example, you could say that as a junior in high school you lobbied with several local community groups to renovate the city's local park. As a result, the park has better playground equipment. Or you could talk about how you started your high school's first culinary arts club and that it now has 50 members since it was started two years ago.