To do list before the start of term

Meet with the professor(s) of the class to clarify your responsibilities. Here are some questions you should ask.
Meet with other TAs (if needed) and clarify each person's individual responsibilities.
Speak with last year's TA(s) for the same course. Collect old problem sets and get pointers.
Build a course website (if needed). Be sure to check if a website already exists. If so, update or re-vamp as necessary.
Familiarize yourself with lab equipment/space.
Brush up on course material.