Here's a quick list of do's (mixed with a few don'ts) for effective essay writing:
Do stay upbeat. Admissions committees generally like positive, lively students. Don't belabor any of the three Ds: Divorce, Disease, Death.
Do make sure that your essay shows your creative side, whenever possible.
Do proofread! Have others proofread! Don't rely on the computer's spelling and grammar checker.
Do make sure your essay has a point. Don't make it a laundry list of everything you've ever done or a chronology of your life. Make sure to say something meaningful.
A quick list of don'ts (spiced up with a few crucial to do's) for effective essay writing includes:
Don't focus on quantity. Quality is preferable. Say what you need to say in as few words as possible. Concise, well thought out essays are the best.
Don't exceed the page or word limit.
Don't overuse the thesaurus. Clear and direct writing in your own words is more impressive than writing tangled up topics with big words.
Don't use trite phases. In other words: "I hope that by learning more about Africa, I can save the world someday." Unless, of course, you can back it up.
Don't aim for a polished, PR statement. Make sure your essay reveals something about you.
Don't brag that being a student at your home university makes you more qualified for admission. Your home university may be well known in your state or region, but the U.S. has thousands of colleges, and it's quite possible that the person reviewing your application has never heard of it