I’ve been working on changes of leads through the trot with one of my TBs who tends to want to travel on the forehand - specifically, pulling along on his inside shoulder rather than pushing from behind. He won’t get heavy in the bit, so if you don’t know, you won’t know – but I’ve found transitions have really helped engage him behind and help lift that shoulder up.
(Some of this might be me-specific, because I am working on my position after years of only riding green horses and never sitting on a schoolie unless it was something I made myself)
To start, I will get a good forward canter rhythm on a 20 meter circle – say I keep it at A. I will circle once, making sure to lift my hands and keep them above his withers. Between the corners K or F, depending on my direction, I will begin to halfhalt and ask for a bit more step under while beginning the change of bend. Corners are where you set up the rhythm and prepare for the change - NOT in the middle of the ring. The trick to a good clean transition is to set up the canter beforehand. Don’t do the transition if you don’t have the right rhythm. It’s the same for jumping – if you don’t have the correct rhythm to the fence, the jump will suck. If you have the right rhythm, the jump is effortless.
At K or F, I will look at the opposite corner and carry my hands and feel my seatbones. I will close the muscle of my thigh to signal to my horse to slow down off of my seat (he is very seat-sensitive) and pick up my hands especially that outside rein (can you tell I tend to carry my hands too low?!). He will break to a trot and my goal here is his straightness. I will post two strides, then sit two strides. During this time, I have set up and changed the bend with some inside leg(sometimes even a one-step leg yield). Once I am sitting, think about looking in the direction of the new bend, signal your canter depart, and use the corner to set up a good rhythm once more.
I do long diagonals versus a true figure eight - which I find is a great exercise once the horse understands diagonals. With figure eights you have much less time to set up the perfect transition up and down – and I’d rather work on setting up the transition to be perfect versus fighting time and distance.