this is the part of the application that I am actually good at (so I was told), so here are some things that helped me:
-first, start writing when you are completely relaxed. Just write everything that comes to mind, don't worry about grammar, content, anything else at this point. Just let your subconsciousness do the talking.
-repeat this until you feel that you said everything you had to say.
-read over what you wrote--not with a critical eye, but rather just to get a sense if you see any common themes emerging.
-create a rough outline
-write another essay, following your outline but at the same time borrowing things from your earlier drafts
-have someone else edit your essay. do it several times, until you have a polished version.
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"To be stupid, selfish, and have a good health are the three requirements for happiness, though if stupidity is lacking, all is lost."
-Gustave Flaubert