Your first priority is to gain a decent amount of clinical experience, working with sick people. It can be gained by volunteering at a free, family-planning, or private clinic, hospice, hospital, VA, residential home, rehabilitation facility, nursing home, or as a first responder, among others. The advantage of gaining clinical exposure through volunteerism, is that it also is looked on as community service, another unwritten requirement for your application.
Nonmedical/noncampus community service is also desirable to have on an application. Consider Habitat for Humanity, Humane Society, soup kitchen, crisis hotline, womens shelter, homeless shelter, or some other cause that is meaningful to you.