Your essay is the best opportunity for you to showcase some of your talents, but it's also the perfect chance to show your passions, your personality, your willingness to grow, or your ethics.
Demonstrate your passions, how the idea has changed you, why this topic or idea has shaped you as a human.
Go into detail - detail beyond what the lay person would know.
Don't just write about your solid grades and strong work ethic during high school - this will go down faster than a lead balloon.
The college essay should paint you as an exciting, innovative, deep-thinking, passionate, and empathetic person with the ability to understand and dissect life situations - showing them to be an asset to campus culture. A moment, a conversation, a game, a class, an interaction - anything. For example, Crimson CEO Jamie Beaton, who was accepted into five Ivy League colleges, wrote about failing at his first part-time job, while Soumil Singh, now a Harvard student, wrote about a game of cricket.