Highlight your accomplishments _ Some of your achievements may not fit into any categories on the application; talk about these accomplishments in the personal statement so they aren't left out. You could also use the personal statement to elaborate on an achievement that you are particularly proud of, but could not address in detail on another part of the app. Think of the personal statement as an opportunity to tell admissions officers anything you want them to know that wouldn't be perfectly clear otherwise. Don't be afraid to brag about yourself; your application is really all about selling a product__you__to the college.
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.