Excite the reader by beginning your essay with an attention grabber (story, quote, details about a patient case or specific medical school memory) that is relevant to your essay. State the theme of your essay clearly in the beginning paragraph or first few lines.
Within your essay, it is important to address:
1) why you are choosing a specific field
2) what are you looking for in a residency program
3) what you are hoping to do in the future within your career (ie. are you interested in an academic career, in specializing, in treating a specific population like the underserved, in health policy, etc.)
4) why you feel you are a strong candidate for that specific specialty.
While addressing these points, it helps to have an overarching theme to tie it all together and help the essay flow. Some people choose to use a patient case or a formative experience in medical school or life that led them to their field of interest.
Be specific. Provide concrete examples that pertain to your life, goals and experiences. Your readers should walk away from your essay with a clear idea of what you are passionate about, who you are, and what type of doctor you are hoping to become. It is only possible to paint this vivid picture of yourself if you use real, concrete examples and details.
The conclusion of your essay should revisit your theme and tie your essay together. Your last sentence should be strong and persuasive about you as a candidate and your hopes for the future.