TONS of transitions.
When I have nothing much to do or take an easy day I always work on refining my cues :)
I do tons of these, they are quite the exerciser and they teach you to use your body more instead of just trotting around poles. Have you tried a canter-halt? Or back up straight into a canter?
Anyway, sometimes I set up some ground poles in a square and practice my square corners with that, it gives you something to look at instead of just practicing the corners with nothing. I also stop off the wall and ask my horses to cross over to the wall, its basically the beginning stages of learning a leg yeild, but I find it relaxes the horse once it has accomplished the task. You also start to feel your own body movements more.