My gelding spends most of his time out in his paddock, so he's walking all day from grazing, and stays warm.
Therefore, he doesn't need a big warmup. He's been moving all day. He's not particularly cold backed anyway, so he's pretty ready to go as soon as I get on.
I usually start off at the walk, and there I'll be doing haunches/shoulder ins, pivots, etc. to get the individual portions of his body loosening.
I'll float him around at the trot a lap or two in each direction, before I start setting him in the bridle. By this time, he's working pretty well, and starting to kick into his frame. I'll do some rating, so I'll go from extending him, and settling in his WP jog, and back up again.
I'll do the same, haunches/shoulder in, leg yields, tight circling, to get him bending.
When I move him into a canter, it's basically the same routine. I'll let him cruise for awhile, letting him move out before I set him in the pace I want.
If I'm working on the pleasure, I really have to let him move out at the canter at first, and get him settled back on his haunches more than I would for HUS, and let him warm up that way, so he's able to go down to his slow pleasure lope with ease. If I don't, he doesn't have the momentum to keep a steady pace.
"You're just as sane as I am."~Luna Lovegood.