State what you're most proud of. Many applications ask you to list your significant accomplishments. Talk about that online tutoring service you started in your senior year of high school, or the $50,000 you helped raise as a volunteer in a United Way campaign.
Go beyond generic job titles. Answer the question "What are your career goals?" by giving detailed and specific information about them. Write that your goal is to specialize in enforcement of immigration laws working for the FBI or the federal Immigration and Naturalization Service--not that you want to "work for the federal government."
Research the college or university to find out why you want to go there. Answer the question "Why do you want to attend___?" by saying that you were attracted by the university's excellent sociology department and the impressive number of its graduates who work in federal law enforcement.