I've been doing basic gymnastic exercises with my very green mare with great success.
They can be as simple as poles on the ground.
The main exercise I've been working on with Ella is 3 trot poles a small jump then 4 strides on a corner to another small jump.
For my experienced rushy jumper I had 2 trot poles 2 ~30cm (1 crate) jumps then a canter bounce to a 2 crate jump, land canter a 20m circle over a pole then back to trot.
Gymnastics are designed to make the horse think; of course they need to suit the horses abilities but poles on the ground in odd patterns are something most horses can handle.