Hi Maddy 🙂
I love hill work and trot/canter poles to make the horse build a lot of muscles. Working in water is also a great option but it requires some equipment aha.
Short gallop sets with lots of trot work in between can be good too, this exercise is also good for your cardio!
For fun exercises, you can work without your hands on the reins, using your legs and seat, then you can ride with a neck rope, I love doing it!