My advice would be to be yourself; let your essay reflect who you are, and capture the readers attention quickly.
My eldest (who had no desire to attend SA's)had a life threatening illness, and used his experience as his essay. He was admitted into several top UC's. Not sure if it had anything to do with his essay, but it definately was powerful.
Another examlpe. My son's friend who was admitted into Stanford wrote about his friends. They have an eclectic group that have been friends since Jr. High. All types of backgrounds i.e., a socialist Russian, a liberal, a Christian conservative, a Muslim, an atheist etc. The wonderful, unique quatlity all these young men had was tolerance. They'd have some passionate debates about their beliefs, yet through all that,they managed to keep a sense of humor, and to this day are all very good friends.
As a note, all his friends are at top UC's. I only know the subject matter of two individuals. Both who captured themselves, their experiences, and their readers early on in their essay's.
I hope this helps. Good luck!