The first sentence of an award-winning essay must look the part. In other words, aim for an award-winning sentence. It can be short, medium, or long, but it must orient the reader in terms of tone, content, and language. Use it to start preparing your readers for the "trip" that you have designed for their benefit (see "Take Your Reader on a Trip" under What Makes a Good Essay?).
Tone. Choose a tone that is appropriate to the rest of the essay. Is this an investigative or instructive essay, or one where you examine different points of view? If so, consider starting with a question. In contrast, if you aim to move the reader through an emotionally powerful essay, consider giving a sense of emotion from the beginning. Or if the point is to delight the reader with an engaging story, use narrative or dialogue from the first sentence. Or if you are entering a battle zone, decide whether you are a combatant or a neutral reporter, and show your perspective in the first sentence.
Content. Just as in the title, the content of the first sentence should be preparing the reader to learn your perspective on your topic. This means, again, choosing a level of specificity that is not too broad. A broad first sentence that suggests a Funnel structure (see Take Your Reader on a Trip) automatically is at a disadvantage. Note, however, that an extremely specific first sentence (even a very carefully chosen statistic), while all but impossible in a title, can be an effective opening. Get right to the issue.
Again, to use a familiar example, consider these alternatives. Not: "Global warming is fast becoming a problem that every nation will have to reckon with." That's too general. Instead, consider: "Not only has the United States failed to ratify the Kyoto Protocol and reduce the U.S. contribution to global warming, but existing U.S. standards for greenhouse gas emissions also have failed to encourage polluters to decrease levels of emissions." This line could set up a thesis statement such as "No organization has done more to publicize the U.S. role in global warming than [an organization whose principles and goals match those of your readers], which has spent ... million dollars to convince me and millions of others that the United States should strengthen its emissions policies."
Language. In the example above, note that the tone is somewhat combative (the essayist takes a side) and that the content is clearly signaled. But the combative language is still respectful: although the U.S. and its emission standards are said to have "failed," the writer does not challenge anyone's motives--perhaps there are good reasons why the failures have occurred--and does not name any specific "polluters." (Furthermore, when you get to the thesis suggested above, invoking the efforts of a well-endowed organization not only shows that the problem has been considered significant but also puts your words in the company of a group larger than merely yourself.) In addition, the vocabulary fits the subject: in an essay that concerns global warming, readers with a good education might expect references to "greenhouse gas emissions" and the Kyoto Protocol. These terms hardly need to be defined for the target audience of readers; the terms help show that you are familiar with the subject. Finally, note that no extreme language is used: the U.S. and polluters are not portrayed as "the problem" but just as contributors to the overall, complex situation.
In any case, the first sentence of a great scholarship essay often is much like the first sentence of a great admission essay or academic essay. See "The First Sentence" in Admission Essays and Academic Essays for further important advice.
Remember that early drafts of your first sentence should be just enough to get you started as you write and revise. Later, when you have a solid command of your argument and a perfect feel for the tone of your essay--this may not be until after you have written several drafts--you can spend time focusing on the first sentence. Don't get bogged down before the rest of the essay is in place.