Select a topic that interests you and compels your imagination. Be prepared to devote a significant amount of time to researching and gathering information, with an eye to analyzing, interpreting and drawing conclusions that are distinctly your own. Steer clear of subjects about which your mind is already made up -- while subjectivity is a feature of essay writing, dogmatic thinking is not.
Resolve to truly think about the subject. Take notes. Sketch out a flexible outline. Read opposing views. Spend quiet time before you sit down at the computer. Once you have acquired a feeling for your subject, start an informal writing process. This is a pre-draft exercise. Writing is thinking and vice versa. You will be surprised at how the simple act of writing triggers thoughts and ideas that otherwise might have remained elusive. Arriving at a hypothesis is a form of rehearsal, a precursor to the thesis.
The thesis is the heart and soul of the essay. This is your core idea and argument and it must be presented within the first few paragraphs. The introduction outlines the subject matter and is designed to engage the reader, but the thesis tells the reader how you feel about the matter. Articulate your thesis clearly and powerfully. And then set out to persuade the reader to see your point of view.
The language you choose exerts a remarkable effect on the tone and substance of your essay. Avoid preciousness, cliche, inflammatory or emotional arguments, trite conclusions and obvious statements. Be concise. Don't give in to the temptation to over-write. Vary the length and style of sentences for the reader's sake.
Build your argument precisely and methodically in a way that makes your conclusion seem effortless--the inevitable end result of all that's gone before it. Include opposing ideas, thoughtfully dismantling them along the way.
Revise. Revise and then revise again. Allow for enough time so that you can put the essay away for a few days before giving it a final read. Errors of grammar and judgment are much more apparent after a brief hiatus and allow for a cooler-headed appraisal. Reading aloud is an effective way to proofread.
Familiarize yourself with your institution's particular style guidelines and follow them to the letter. Cite sources. Credit properly. Don't undermine the quality of your effort and work by failing to accede to basic academic requirements.