Did you know that the new SAT (debuting in March of 2016) has a new essay format? You now have 50 minutes to write, and the format has been totally revamped.
If you would like an example of what the College Board is looking for, then it helps to read some sample essays first. There are some in the new SAT book, and now I've chosen to write a sample essay of my own as well.
I strongly suggest that you write the essays by hand using the blank essay space provided in the book, to get a feel for the length and the timing. Most of us can type faster than we can write, but for now at least, the SAT is still a paper and pencil test.