Another important thing is find a group of individuals that is doing the same thing so if one of you finds something groundbreaking you can share it with the group. That could be lots of opportunities, a group to study with, they may find a professor that helps with grad paperwork that you then have a connection with.
These are two things I wish I did in college as they were there and free! Also make sure to find the requirements for grad school to ensure you got them covered.
Angel, it's terrific that you are being so thoughtful about preparing for a field in the law. I've never been a prosecutor, however, I know many and have some thoughts. First, work hard and do your best to get good grades. One of the clearest paths to success in the law is success in school, including your undergraduate studies. And, of course, the better your grades -- and LSAT scores, and extra curricular activities -- the more options you will have for law school and beyond. Second, pursuing studies or classes in political science, criminal science and English are important. Third, focus on your presentation/oratory skills -- get involved in debate, Model UN, or other opportunities that challenge you to think and speak on the spot. Fourth, consider leadership opportunities -- including on-campus or with community groups -- that build both your leadership skills and your community focus. Fifth, dedicate yourself to your writing skills -- they are critical in law school and any legal career, particularly one that involves the courtroom. Finally, consider an internship or other opportunity with a local prosecutor's office. You could learn a lot and build further exposure to the field. I wish you the best of luck -- we need more dedicated public servants!