Admissions officers read hundreds, sometimes thousands, of applicant essays about how, for example, "Soccer taught me the importance of discipline and hard work." That statement, however, provides little information about exactly how soccer taught you discipline and hard work. Don't spend the entire essay detailing every grueling workout, but do explain how your thinking and outlook changed for the better.
Focus on a single, meaningful moment you had while volunteering in Kenya or New Orleans instead of reporting every emotion, action and resolution you experienced over the particular two-week period in question. By focusing your essay, you can fully develop the clarity of language and richness in your descriptions needed to distinguish yourself. Admissions officers don't expect your essay to reveal every facet and trait of your personality, but they do want to see clear, concise and thoughtful writing.
Write about something that is truly unique to you. An essay describing your passion for making soup can be just as informative and interesting, sometimes even more so, than an explanation of why you want to become a medical doctor. Essays that capture your quirks, work habits and interests in everyday life provide a rare and honest glimpse of who you are as an individual.
Everyone faces challenges and struggles, but some obstacles warrant more page space than others. Detailing the strain of jet lag and dirt-floor lodging on your youth group's trip to Mexico can seem whiny, especially compared to the essay of an African refugee who hid from rebel soldiers in a dirt hole for two-thirds of her childhood. Instead, write what you learned about yourself while sleeping on that dirt floor or bartering in a foreign market.