An effective TA should create a comfortable atmosphere, identify goals, give direction, encourage participation in class, be organized, be responsive, and give feedback.
Classes should be conducted and material presented in accordance with objectives of the instructor to whom you are assigned.
TAs whose responsibilities are grading should establish clear, firm, and consistent objective standards for evaluating student performance and should assign grades only on the basis of those standards.
Make yourself reasonably accessible to students by keeping regularly scheduled office hours.