Getting into medical school has gotten so competitive that it's increasingly important to have a strong candidacy with excellent grades and robust extracurricular activities starting early in your college career. As I've mentioned in previous blog entries, one mistake I see pre-meds make is that they are so focused on leadership and research they forget a critical component - clinical experience. To prove you want to be a doctor, it's essential you obtain clinical experience for a significant period of time - not just a health fair or two. Good grades will not make up for a lack of clinical experience.
Working as an EMT, in a good clinical care extender program, or in a low-income clinic are just some ideas for obtaining excellent clinical exposure. (Although you might think free clinics would be thrilled to have a pre-med volunteer, many understandably require one-year commitments.) Shadowing is a mixed bag: Medical schools don't know whether you're second-assisting in the operating room or just standing in a corner being ignored. If you choose to shadow, make sure you strategically highlight your clinical experiences in your written materials. Other popular options include international clinical work (although it is usually short-lived) and working as a volunteer in a hospital (although it might be more clerical than clinical, depending on the position).
Do your research before accepting a "clinical" job so you ensure you'll really get the experience you need to confirm to yourself that you've made the right career choice (very important) and to show admissions committees that you can handle the heat.