Become pals with at least one person in class. If you have to miss a class, you can catch up much more easily-find out what you missed etc. Become pals with the teaching assistants. They are smart and have good tips for studying etc. They also remember what it was like to be an undergraduate in a large lecture class.
Large classes require rules that are inflexible.
If you have a special situation, come talk to us about it. If you leave early, your name will be taken by the teaching assistants. If you leave a second time, you may be dropped from the class, or your grade will go down by one letter grade. Whisperings magnify in large classes - do not talk to your neighbors during class so that your fellow students can hear. Repeat offenders will be asked to leave the lecture.