I had a trainer tell me once that horses are actually pretty comfortable in a routine (to an extent), so he does the same worm-up routine at home that he will do at a show. And that made a lot of sense to me! So on my more broke horses, or the ones that are getting close to getting to the show pen, I start all my rides basically the same.

1) I rarely lunge. I may not have time or room to do it at a show, so unless I haven't ridden in a few days and my horse is ornery, I avoid it.

2) I get on and stand still for a few moments. Nothing I hate more than a horse that moves off as you're getting on!

3) Walk a lap or two around the arena, working out kinks and warding to warm up the muscles. The start asking my horse to bend and flex thru the neck, maybe walk a few circles each direction.

4) Move up to a jog or trot, and follow the same routine as walk.

5) Ask my horse to stop and back. Walk another lap or two. Then ask for a lope. Follow same routine as at the walk and jog.

That's my basic warm-up routine. It takes maybe 10-15 minutes, so I can always fit that into my schedule before my classes. After we're warmed up, then I start working on whatever goal I've set for us. It may be lead changes, counter cantering, leg yields, serpentines, transitions, extension and collection, etc. I usually leave some cones and ground poles out in the arena so I can make up a pattern to ride (the difficulty depends on the horse). We work on opening and closing the arena gate while mounted, I'll go ride out in the pastures, take a walk down the road, etc.
We always start a working on a long and low outline. Rowan is kept indoors for the most part of the day, so she usually needs a little extra time to work out kinks and just stretch. She's a pretty high-strung horse; so working on relaxation really helps to make a more enjoyable ride for everyone involved.
Then we do all three gaits, working changes of direction and gait. We usually finish up our warm up with lateral work. Then it's on to schooling whatever we need to work on that day, and we end with a loose-rein walkout.

We rarely change the routine, just because it works so well.
I try to change up the routine depending on how BMOC looks when I get to the barn. If he's looking stiff (because it's been like -2 here) then I will walk him bareback for maybe a half-hour, so he limbers up but doesn't sweat. If he's fresh (which is most of the time) I do a lot of lengthening and shortening exercises, bending, serpentines, etc. Hopefully, on the day of a lesson he's somewhere in the middle, lol
Right now due to inconsistent weather I'm lucky if I can ride 3 times a week, but here we go.

Storm: Ridden about 3 ax’s a week, 2 days of serious flatwork with half-passes, and shouldering etc. The third day is an hour long trail ride followed by mossy around the barn area and some carrots in dinner...

Mocha: Ridden about 3 times a week, 2 days flatwork, 1 days is strenuous the other is just focused on shortening and lengthening strides. Third day is a quiet hack (although with all the turkeys around nothing is quiet).

Red: 3 times a week, nothing real strenuous as he is still growing, but 2 days flatwork focusing on transitions. The third day starts out with flatwork then ends in a little trail ride.