It helps when a student goes to a TA and the TA knows exactly what the professor talked about because the TA took notes from the lecture. When TAs don t attend the lecture and the student has a question regarding the lecture content, the TAs don t know what the professor talked about and thus cannot effectively help the student. They, then, have to make an educated guess as to what the meaning of a certain concept was. Second, TAs should hold offices hours and stick to them. Several times I went to TAs' office hours and they never showed.
Accessibility is an important factor in effectively helping students.
Third, TAs should be enthusiastic about their teaching and their subject matter. When TAs seem to enjoy what they are doing, the students find it easier to approach them for help. In short, I think the main things that make TAs successful and integral contributors to the education of students is their friendliness, their willingness to help, their availability, their organization skills, and their motivation. All these things count in the eyes of students. So often professors are too busy to answer each student's questions and large class size inhibits students from asking questions in class.