Make sure you attend the very short presentations given by all professors in the department. This is a very useful first step on your way of finding your research field and supervisor.
You should have a reasonable standard of living. Please make sure you know your rights. (personal anecdote)
As part of your financial support package you are entitled to Research and Teaching Assistantships. Please note that you are automatically a member of the Union of TAs and sessional lecturers at the UofT
Each September there is a TA training workshop in our department in which you will participate but if you feel you need more help to be confident during your lab sessions or tutorials. There are good resources on campus, available to you for free through the Student Affairs.