What's the key to a winning personal statement?

The key to a good personal statement is 1) a good, clear, structure with each paragraph dealing with different aspects of your application, and 2) that every claim you make about your strength of character, your personality, or your academic abilities are backed up by examples. I.e. every time you make a claim like 'I am hard-working', make sure to give the academic some good examples of how you are hardworking. It seems obvious but you'd be surprised how often people mess up their applications on such simple points.