As above posters said, use the Kaplan Method. Its quick and easy, and even if you get stumped on one essay if you have good writing skills you can pull out a Q. But for the Kaplan Method to give you a Q+, you need good examples.. or at least examples which you can explore in the prompt. Just have some broad ideas or concepts, possibly about topics you enjoy or already know much about that can fit into the usual MCAT prompt of business, politics/sociology, technology, or the "X is more important than Y, when is it not?".
Some examples: historical figures, great depression/FDR, civil rights act of 1964, Apple, etc.. things you know well though, not necessarily these. I had some of these que'd up like a rolodex and just pulled out whatever fit the prompt and it got me a Q or R on my exam dates.