Fraser: Find a topic that you sincerely believe in, then write. So many people talk about getting things done, but never follow through. When my teacher told our class about the Award, I went up to her at the break and said "I am going to win this." She said, a little hesitantly, "Well, put your entry in and see what happens". I responded, "Ok, but I am going to win. For sure." I think I told my parents that I would win before I even knew what I was going to write about. People call that arrogance, but I believe it's important to have confidence in your abilities to do a job, whatever that job happens to be.
Matthieu: The most important thing, of course, is to read the essays of past winners. This will give you a good idea of what the awards committee is looking for, and also of subjects that have been previously explored. Next, take a look at the judges and note their backgrounds and professions. I don't mean to say that you need to cater to their sympathies, but it might help you choose how to write your essay. In this case, after reading about the selection committee, I decided to eschew a hardcore academic style (even though some of the past winning essays were written in this style) and write something more similar to what you might find in the Op-Ed section of a newspaper. It's a more comfortable style for 2,000 words, for me at least, and I felt confident that the judges wouldn't punish me for it.