As David said, it depends on what you want to improve. Do you want you horse to jump higher or better?
Your horse jumping skills comes from genetics, if he comes from a good jumper family, it will be easier for him to jump.
But you can also work with him on mechanization lines to help him be more reactive.
Then you have to work his suppleness on dressage with for example shoulders in or half pass (it depends on the dressage level of your horse of course).
What exactly is his flaw on jumping?