Each school is looking for something a little different from its applicants, and the questions are designed to garner that information. So careful attention to the language of the question pays off. And some prompts are really general, allowing you a lot of room to maneuver. Be sure to include information that will be helpful in the evaluation of your application credentials. These help your mind come up with concrete details, so that you can show an admissions committee something about yourself, not just tell them the surface facts.
First impressions count, so take the time to think of good details to include.
When you have your details, then make a scratch outline of your answer. Only then should you begin writing, developing your essay according to the outline, and sticking clearly to the topic you've been asked to write about. Use details, examples, names and places to make vivid word pictures of the person you are and why you are applying to this school. Add transition words to give a strong sense of organization to your readers. It's important, of course, to be totally honest in these answers.