Fact: Your essay is the key to your scholarship application. It is an opportunity to demonstrate to the selection committee that you are a well-rounded individual, that you are more than your GPA, that you are a strong writer, and it gives you a chance to talk about your experiences and qualifications in greater detail than what appears on your resume or transcripts.
Many schools and other organizations that give out scholarships will give you a "prompt" or a question which the essay is supposed to address. Read the question or prompt carefully and try to "read between the lines." For example, the prompt you are to answer might be, "Describe a book that made a lasting impression on you and your life and why?" Ask yourself, "Are they really interested in my literary preferences or is there something more to this question?" More than likely, they want to get a better idea of who you are—not only what types of books you like but also what motivates you and what sorts of stories or topics interest you. They may also be interested in getting a sense for how promising a student you are based on the type of book you choose and what you have to say about it.