When the athletic standard of a group is very high, as a coach, it is lots of fun because you can push them pretty far. However, group fitness, in a commercial gym, is like a box of chocolate, you never know what you’re gonna get.
You need to be skilled to regress every movement to its basic component. I think its important to master the Explanation, Demonstration, Imitation and Repetition pattern repeatedly. Why move on to a harder exercise if your group isn’t excelling at the basics? Only Perfect Practice makes Perfect.
The same goes for your own training. Understand your own motivations for going to the gym. If you don’t feel 100% that day, adapt your plan. It’s important to have a training plan but don’t be afraid to toss it out if you have to.