For myself, one of the harder parts of my partnership with my horse is our differing goals. I often envy pairs ice skaters, where both parties are firmly agreed on a common ending. With my horse, the struggle for me is to encourage him to work happily for me, always improving his work, while recognizing that all he really wants to do is eat and roll in the dirt!
The best way for me to keep my mounts' work at least not annoying is for me to be unobtrusive in my riding style. Although I hold him firmly to leg means go now, much of the rest can be suggested and then rewarded. There is no way to hold a carrot on a stick in front of him, but if responding to my whispered requests is not too hard, he generally is happy to go along with the program.
I must always be sensitive to his feelings though. If he feels the work is too hard, boring, repetitive etc. then it is up to me to recognize his concern and respond. Perhaps the same work but out in a field or on the trail and not a ring. Perhaps company around, even drill team riding. Perhaps work needs to be abandoned on occasion in favor of a simple gallop up a long slope for a workout. Horses do not ever seek perfection the way I do, and I must always be aware of their complex emotions and desires to achieve my own goals.