This is all dependent on the exercise modality. Forms like yoga and pilates will vary less as there are staple sequences and poses that are usually always present. If we’re talking general fitness resistance based classes theres a lot more “flexibility.” (pardon the pun). That being said, members like consistency and the body needs something familiar through which to progress at the same time that it needs variability.
I would develop a few signature moves that will always be present in your classes. Something members can judge their progress with and they will also find familiar and comfortable. For spin, maybe thats your last or first drill. For resistance classes maybe theres a challenge built into each class thats the same week to week.
Sometimes we get to complicated because we think the members are getting bored, when really its us. Creating complicated movements for the sake of “freshness” doesn’t alway work to the advantage.
Changing day to day isn’t necessary. Changing week to week or cycle to cycle (4-6 weeks) is. Too much variability is not always good, too little the same.
Music changes everything. If you don’t want to change majority of the movements, change the music! Amazing how that can create a completely different feeling and have people forget that they’ve “done that class before.”
Also, you teach everyday, they don’t take everyday. You may have taught the SAME class 5 times, but odds are they’ve only taken it 1 or 2.
I hope this helps, I can go on forever as you see, so if you have any questions don’t hesitate to reach out.