Aside from what's been said:
-Wear ear plugs.
-Don't worry about dragging your knee.
-Take the time to learn the line around the track, paying attention to your reference points for braking, gear changes, turn in, etc.
-Don't be afraid to ask the instructors questions. No question is a silly/stupid question.
-Take a notebook. Write down what you learned, what the line is, what your reference points are, what changes you made to the bike.
-If at any time you feel uncomfortable, rushed, startled, or just feel something isn't right, pull in and pit. "XX minute sessions" doesn't mean you have to be out there for the full session, it's just a limit.
Before you break for lunch:
-Ask if there will be a track walk with an instructor. This is where an instructor takes you around the track, explaining details about difficult (or all) corners.
In the afternoon:
-As people get faster, there may be an increase in the number of riders clumped together. If you have trouble passing someone, or if someone won't pass you, pull in and do a ride-through of pit lane (observe pit lane speed limits). This will put you in a different spot on the track, away from whatever rider was bugging you.
-Remember to give the appropriate hand signal before leaving the track.
- If you feel comfortable with what you are already doing, start saying aloud what gear you are in as you shift. You'd be surprised how many seasoned track riders don't know what gear they are in. Why is this important? If you ask an instructor how to improve something you are doing on the track, they will ask you - especially if your question is about getting through a corner.