She will be self-motivated and hard-working.
On exams or essays, she will not provide the regurgitated answers that most students write. She actually thinks about the course material and the broader issues raised by the lectures and readings. When she raises questions in class, they are informed and sound like research questions.
She is an excellent writer.
Excellent response.
I'd add that the student is secure in his/her own work and doesn't have a need to insult or be rude to other students during classroom discussion is also a good candidate.
A student who is preparing for life beyond school is also a good doctoral student. Before graduation, students should be involved in some aspect of running a conference (even as a volunteer), be a gracious host/hostess to visiting profs and not a star-struck student, represent the department in university activities, understand how to work with support staff and get things done. There is life after grad school; in addition to finishing the dissertation, PhD candidates should be preparing themselves for life as professionals in their fields.
