This is the most important thing to do in your medical school admission essay. In the AMCAS statement the key thing to keep in mind is to provide specific examples when you are describing your strengths and what you bring to the program. Provide details in the form of the names of the doctors you shadowed, the focus of the research you performed, the names of any associated publications, and the specific names and settings of the places where you volunteered.
In order to leave your indelible mark, you must make a connection with the reader. A connection isn't necessarily forged by the fact that you saved the world from famine, or that you won the nobel prize for literature. Something that is significant to you, can and should come across as significant to the reader. Here's an example from a medical school admissions essay:
Writing Your Medical School Admissions Essay - MomMD