FORMAT. My SAT essay format, which has given many of my students 6s all around, has been this: Intro, Example 1, Example 2, Conclusion. The Intro introduces a unique take on the idea. Example 1 is from literature or history. Example 2 expands Example 1 with a personal example or through current events, into current times or pop culture. The Conclusion is not a repeat of the Intro or simply a summarization, but rather gives an independent thought; something to think about; a "moral to the story," if you will. Ideally, you want an essay which starts off answering the question from proven sources and ends up asking a creative rhetorical question back to the graders which makes them think so much they have to smile at your mastery of the subject. And give you a 6.
GRAMMAR. Essays are graded on a holistic standard, meaning that the graders are not supposed to take into account your crappy grammar. However, they do. They are human and they are the final say. So if they read 50 essays before getting to yours and then they can't understand yours because of the chicken scratch handwriting and ridiculous grammar, they'll grade you lower than normal. So go over your grammar rules and test your handwriting before you go in there to the SAT test. Don't get docked because you didn't care enough to pay attention to details.
RESOURCES. Another thing that will impress the judges in the less than a minute time frame that you have to impress them is NEW SOURCE material. I mean, how many essays can you read about "Was the Iraq war fair?" and everybody quoting 1984 from George Orwell about Bush being Big Brother and Saddam Hussein being Goldstein? Read a book that's not on your summer list. Have some new sources for that first example. And when it comes time for Example 2, the personal example, don't hold back if you've got something juicy. You can change names to protect the innocent, but remember, the graders are HUMAN. Throw them a bone. Give them something worth their time to read. The deeper you go, the better you'll do. Take it from someone who graduated Ivy League. I promise.