What classes have you GSI-ed/TA-ed for? Have you been the instructor of any courses?
What have been the biggest challenges that you've faced while teaching?
How do you balance teaching with all the other demands of grad school?
In your teaching experience, what strategies have you found to be effective? Not effective? (e.g., different lecture styles, type of homework problems, projects vs. exams, etc.)
What do you like best about teaching?