Keep it quiet. Exercise your jaws outside of class, not by talking during class. And those grunts and moans are unnecessary, theatrical and distracting. Rest those cell phones and beepers. They should be turned off or on silent mode.
Cleanliness is next to godliness.
Keep your cool. Group classes operate on a democratic system. Forget flying solo. By definition, classes are group activities. Consider others' exercise space and don't crowd someone who has arrived in class before you.