My programme design is simple. Everyone needs a deep knee-bend, to pick something heavy up off the ground and put something heavy overhead, to brace their trunk while doing so, and some people need one or two other exercises to deal with injuries or postural issues. And then they usually need to get their heart rates up. And afterwards stretch, though everyone ignores that part.
- squat/lunge
- push
- pull
- [maybe] corrective
- [maybe] cardio
- stretches
The only question is whether they're using machines, bodyweight, dumbbells, barbells or whatever. Which depends on their capabilities and goals. I mean some people are so deconditioned that they just can't squat below about 45 degrees above parallel. So okay, leg press for them for the first programme - since there are just 18 spaces to record workouts, so it's a month or two only. And others could do barbell stuff but won't be confident doing it, or simply won't want to - but will be happy with bodyweight and dumbbells.
Once you have that basic template in your head, provided you know the exercises you're fine. Train movements, not muscles and everything becomes much clearer.
If you think of muscles not movements you end up with routines with 12-18 exercises and cable shoulder internal rotations and medicine ball walking lunges with a twist and dead bugs and bicycle abs and dumbbell lateral raises and swiss ball crunches and all this other shit that I often don't know what it is and even when I do it confuses me because I have been punched in the head too many times in my life and I have to keep things simple or I get upset.
I mean to begin with, just fucking let them squat, or at least leg press with their feet out, they feel their arse and hamstrings working for the first time in their lives and are startled and insanely grateful.
For the vast majority of gym-goers, it's really not that complicated.