Writing essay exams is part art, part science..
The science part is the easiest bit — make sure you take apart the questions and answer every part of each question. Make sure you understand the question, look up any unfamiliar terms and generally know what the heck you’re talking about.
The art part is more difficult — you should weave together your own original observations, include original examples and be sure to give clear and compelling analysis. That’s tough — so, good luck!