Specific writing reveals more about you and is easier to prune than a series of vague descriptions. For example, don't simply write "basketball taught me the value of discipline and hard work." Rather, explain how and why basketball taught you these lessons by describing a particular instance. Focus on a single experience or moment, not just a general overview of your most grueling practices or demanding coach.
Admissions officers read hundreds, sometimes thousands, of application essays each year and can quickly detect insincere or inauthentic writing. If you want to be a doctor, don't just write your essay about your desire to help people. Go deeper, and honestly describe your fascination with the workings of the human body. Write with honesty and conviction rather than restricting yourself to what you think they want to read.
Choose a writing style and topic that best fits your personality. Some students are serious and methodical, others are spontaneous and excitable. If you have a good sense of humor, include that in your essay, provided it's appropriate to your topic. If you're not a naturally funny person, now is not the time to start. Remember, the college essay has no single "right" form.
Proofread several times. Don't just rely on your computer, which won't always catch the misuse of words like "form" and "from" or "later" and "ladder." Detecting errors in your own work can be difficult so have a trusted friend or teacher help you by making mechanical or content edits. Don't pass your essay out to everyone for review; too many opinions can ruin a piece. Stick with a few trusted individuals and your own good judgment.