Ariadne gave you some very good tips. For exercises use your imagination and after you get a first feeling/impression of the class, the participants, their fitness level and first impressions you will have a better idea of how to continue with the rest of the class as well. Keep your mind open and always have alternative exercises for those participants who cannot perform a specific exercise/moves.
One routine out of the box which you can incorporate into your regimen, is to take the class for a walk or even a run/jog if they are up to it (carrying their bosu ball). Then every few minutes or a certain distance have them perform a number of exercises (either counting repetitions or for time) and when done move to a different location. Keep repeating this for the whole session. This will improve their stamina, burn calories, make it more exciting and fun and it will give them time for some active recovery between their exercises and their walk/jog.
I hope this helps. Good luck.