Obtain and read the guidelines for writing a personal statement; note that applicants are left with considerable latitude to choose what they write.
Think carefully and honestly about why you want to go to medical school: examine your motivations, your history and the process you used to decide to become a physician.
Choose a theme for your statement, which may describe a life-changing event, an important relationship, or a specific aspect of the practice of medicine that appeals to you.
Write the statement, taking care to avoid remarks that might convey arrogance or offend. Write a complex statement that demonstrates your ability to grasp the complexities of medicine.
Ask another person to read, revise, and evaluate the essay honestly. Pick somebody who will tell you the truth.
Revise your essay to reflect feedback. Polish it. Leave it untouched for a week, and then return to it and revise it again.