The interviewer wants to hear that your past employer will describe you in a positive manner. Think about the positive things your former employer has said about you in the past. Instead of listing these things, tell the interviewer what each person has told you. For example, you might say, "John has told me that I am a hard worker, and he has told me that he really likes how I am always happy to be at work!" These concrete examples will be sure to impress the interviewer!