The interviewer is really asking, "What makes you stand out?" Think of your top three greatest strengths. Maybe you are positive regardless of the circumstances and can cheer others up when they are having a bad day. Or maybe you are an expert at handling conflict, within a team or with customers. Write down a few examples how your strengths to help them sink in. This will also give you more to share at your interview, making your strengths more tangible to the interviewer.