You do not have to get it right the first time! Instead, write the first draft of your essay with the main focus on content; communicating your thoughts. Then set it aside for a day or two, reread it with a fresh perspective, and make any necessary changes. This is also the point at which you should consider matters of organization, style, grammar, spelling, and tone. Once you have rewritten your first draft, you may wish to try it out on your family, friends, English teacher, or college counselor. While the final product and final "voice" should be yours, they may be able to offer helpful suggestions for technical or other improvements. Within this general outline for actually writing the essay, there are some "do's" and "don'ts" which I would like to highlight.
Your college essay, along with your high school record, standardized test scores, and extracurricular involvement, will provide the basis upon which the college makes its admissions decision. A thoughtful, well-written essay can affect in a very positive way that final decision. Keep this in mind and take full advantage of the opportunity which the college essay affords you.