Medical schools have a specific set of prerequisite courses required for admission so most applicants will come from biology, chemistry, biomedical engineering, and other sciences majors; however I have met literature majors, theater majors, and history majors during my time working for a medical school. As long as you have the grades and test scores to indicate your academic strengths, you are off to a good start.
In addition to grades, you will want to get hands on experience. Whether you are volunteering in a hospital and transporting patients, coloring with children in a pediatric unit, or answering calls as a receptionist - you will want to have an understanding of what it feels like to be in this profession. You may also want to interview a doctor or someone else in the medical field to get a "day-in-the-life" understanding and learn some do's and don't's