The body of your personal statement is going to be hard work _ you need to use around 50% of your word limit to give the admission representatives concrete evidence of why you stand out from the crowd in this application process. The body is also where you will be answering questions and giving examples of experience and affects of experience. Answers and evidence need to keep reflecting who YOU really are. If you're struggling to keep under the word limit, allocate each question a word limit as well.
Avoid Cliches. There are a few standard reasons why people become doctors, and so it is very easy to fall into cliched expressions and ideas. Though it's fine to express a commonly_held notion, try to find a personal way to express it. For example, rather than write "I want to be a doctor because I want to help people," discuss the ways that you have shown your generosity and kindheartedness in the past; bring specific examples__such as your volunteer experiences__so as to avoid a direct (and possibly cliched) declaration of your point. Sometimes cliches are unavoidable; just make sure your essay isn't full of them.