Someone who is "down to earth" is someone in touch with the lives and realities of ordinary people. No matter how high a person's social status, if we say that person is "down to earth," that person does not behave in a way that is separate from the average person. Example: "Louse makes a lot of money, but she's very down to earth. She treats everyone like they're important and doesn't act arrogant or spoiled whatsoever." This phrasing is meant as a compliment.