Get them moving away from your leg (e.g.. turn on the forehand, leg yield). With the leg yield start by teaching it at the halt and when they understand and can carry out the movement capably try it at the walk and so on. A variety of smaller 10m circles to bigger 20m circles is good for getting the horse to use their body correctly and bring their hind leg underneath themselves, it also helps with bend and suppleness. Make sure you do heaps of transitions and changes of rein so they are listening for what is coming next and focus on you. If you want you could also add some pole work (ie. poles on a circle, poles in a line with a larger trot stride in between them and then another line of poles with shorter strides to make your horse and you think and work to shorten and lengthen your stride/collect up and push out.
I love how you can add poles to every exercise and make them more interesting to you and for the horse 🌟 Transitions between them, longer and shorter pole gaps for stride collection, lead changes, getting that hind end working... the list just goes on and on 😂
I love starting with a working walk for a good lo or two each way with some leg yields to get my horse really thinking about my leg. As we trot I love incorporating circles, serpentines, changes of direction and leg yields. It's also important to practice collection / extension❤️
Theres always so much to do with flat work!
I really like to canter in a small circle at the canter, if you think they can balance themselves enough, and do walk canter transitions in a small circle to make them really use their hind end. I also like to extend and collect at all three gaits to get them responsive. Lastly, I love doing trot and canter poles on the ground to really start getting them thinking. Hope this helped! 😊