summer after frosh year in college i did research/shadowing for 1.5 months. then summer after soph year. wasn't until junior year that i kicked it into full force tho and did research during the year and the summer. this year i've done nada.
I started volunteering in the patient transport department at my university's med center a month into freshman year for 3-4 hours a week. I basically did it because I wasn't sure what else to do that was medically-involved at the time and because I didn't have any connections.
After sophomore year, I started doing research at the medical center. It was through the research that I found some shadowing opportunities in a variety of fields.