Writing a personal essay
Remember, when you're writing a personal statement, that you aren't just writing a simple list of past and present successes. Your personal statement should reflect who you are, what you want to accomplish, and what your plans and dreams for the future are.
Your writing should tell university representatives that you, the institution and your area of proposed learning will be bettered because of what you want to study or research. Don't sell yourself short. Make the people reading your essay know that they'd be fools not to accept you. Make every word count and allow every word to reflect who you are and what you know you will achieve in the future.
As far as essay structure goes, I didn't really follow one. The only advice I was given was to 'sell your whole self and not just your accomplishments'. Other than that I basically just created my own format. On the most basic level, I'd say definitely build a really strong opening/introduction and a solid conclusion. Create an outline for yourself ahead of time so that your thoughts and ideas aren't scattered. And EDIT! There is nothing worse than a beautifully structured essay with grammar mistakes.
Other than that, make your readers want to know you, talk to you and make them remember you.