Preparing for your first week
Policies your lecturer should tell you about
You lecturer should definitely tell you about overall grading policy, including how your discussion section fits in, and calculator use during tests. These are the first things your students will ask you about. Some will also tell you what your homework and quiz policies should be, others will leave this up to you. As you continue to TA, you will see that lecturers range from very "hands off" to very "hands on." Regardless of how your lecturer wants to do things, they are right. If you disagree with them discuss it privately with them. If you still disagree with them, do things differently when you're a lecturer.
Another topic that your lecturer should address at some point (not necessarily during the first week) is regrading test questions when students have disputes. If your lecturer does not have a policy, a good one to follow is to find the TA who graded the problem in question and have her or him look at it again. Don't be afraid to be stingy with regrades! If you get a bad (for you) reputation, you may end up facing a mob of students trying to take advantage of you. Many times it is enough to tell the student why they got the number of points they did and to point out that this happened to many of the students in the lecture. If the student understands that the grading is fair (albeit harsh), they will usually back down at this point. Another tactic which you may see is that a TA will tell the student that they will only regrade the entire test and not just select problems. This usually appeals more to the student's fear than reason, but that can still be a powerful motivator. When all is said and done, though, regrade following the lecturer's policy.