Most college applications prompt their applicants with a question or statement that they would like answered or expounded upon. Rest assured though, you don't have to let this hold you back. In fact, these prompts can give you the opportunity to demonstrate your creativity. Think about the prompt for a while and approach it with a fresh perspective. For example, Dartmouth's prompt is: "If you were to describe yourself by a quotation, what would the quote be?" The basic response would be to choose a quote and then list why you are like said quote. A truly inspired essay, however, would tell a story that relates to the quote and proves how you are like your chosen quote. This will engage the reader, prove your point and show that you can illustrate a concept without merely listing attributes.
In the rare situation that you can choose a topic on your own, pick something that you are passionate about or enjoy. Keep in mind that the purpose of the essay is to demonstrate that you have a mastery of the English language and to show what you are about, so although it may sound like a cliche, write from the heart. Share a humorous adventure you had with friends that taught you a life lesson. Or talk about your first job and how terrifying it was, and how you overcame your fear. Recall your first date and what you learned from it. No matter what you choose, be sincere, be to the point and try your best to reflect your personality.
It's key to understand that writing a college essay isn't about writing the perfect paper; it's about showing the college of your choice who you are. No matter how unique a topic you choose, if the essay is not well written and sincere, you will get little response from it. Don't ignore the rules of composition, but more importantly, don't lose yourself in the fear of pleasing the college.