Once a spin "instructor" at our gym had people put the fronts of their bikes up on the plastic blocks used in the step classes. don't do that, 'kay? (things like this happen when management throws any trainer on a bike to lead a class, I hate it.)

And be aware of your warm-up needs. Take the time you need even if the person leading the class wants you at 75% in the first five minutes.

It is possible to hurt yourself on a spin bike, so when something doesn't feel right, stop doing it. There's the "pleasurable" pain of working your muscles and lungs hard, but joint pain IS a no-no. For example, some instructors have us do jumps - lifting up off the seat to a forward position and sitting down again - in quick succession. I have a knee that hates them - but I can do every OTHER jump & concentrate on form/control.

Drink lots, even if the instructor isn't cueing you.

oh, and stay off bike 18. That's my favorite.