The best students come to class with an open mind and a willingness to learn. Why else come? Training is all about learning. Teachers learn from their students and students learn from their teachers. The failure comes when either one thinks that they can't learn from the other.
Everyone is a student and the best students know that there is something to be learned from every person, every situation and every thing. What really clouds our ability to learn is our ego. Our ego thinks, and that is the problem, that it is somehow above someone or something else and thus shuts off our ability to be objective. This lack of objectivity is what keeps us from learning and growing. In life there are no absolutes because absolutes are a matter of perspective. To be able to "see" is what enables us to learn. To be only able to "see" a certain way disables us from learning.
When students show up at the dojo, they should be open and willing to learn. These are the two traits that all good students (and teachers for that matter) have in common.