A few things to keep in mind about SAT essays:
1. Critical thinking - you need to offer a logical opinion, supported by valid reasons.
2. Develop one main idea, your thesis. Offer multiple defenses and exemplifications of that one central idea.
3. Use clear language. This doesn't mean simple language; it means one should not be confused about what you are trying to say. The grader of your essay will spend very little time reading your essay. They do not want to ponder deeply on your essay, they want to understand it on the first pass.
4. Vary your sentence structure. Use a mixture of longer complex sentences, and shorter direct sentences. Don't do this simply for the sake of variety, although that has some value in itself. Do it to help make your point clearer, and your position stronger.
5. Make sure the examples you use to develop your main idea are clearly appropriate (they are on topic, not just tangentially related to your topic).
6. Your thesis should not be obvious; it needn't be amazingly insightful, but it should not be a cliche'. It should be contentious enough that someone could have a different point of view, while still respecting the merits of yours.
I'll give you many more such posts on essay writing in the future. This is just a first run that introduces some of the vocabulary that SAT evaluators use when describing a level 6 essay.
