I'm not going to lie and say that I don't judge people by way they look. Because I do. So, ideally, I don't judge on looks, but I know I do and I will own up to that.
As for music? Well, usually if someone listens to a type of genre I know a bit of what they are like. For instance, if you listen to Disney music, you're probably cheerful. While, if you listen to people screaming about death constantly, you're probably not the most cheerful person. Music speaks emotion, and puts what you're feeling out there. So you get a bit of what a person is like and what they are feeling by what they listen to, but you shouldn't necissarily judge them that way, and what they are listening to isn't always true to what they are feeling.