Flatwork should take up 75% of his training.
Take him on trail if that's available, and walk uphill, trot downhill. Make sure the footing is stable, and don't let him rush. The purpose is to strengthen his back muscles and hindquarters so that when he jumps, he is using his "engine" and not his forehand.
Talk to your trainer about a schedule. For my horse, it is a full on jumping school lesson once a week, and he is ridden 3 times in between.
Ripley, another, has flatwork 4 days a week, light jumping each time. I'm talking about less than 3 foot verticals, and 4-5 circuits jumping it once. That said, Ripley is very seasoned and not showing lately, so it is easy and gentle for him. Jumping is just for fun for us (Ripley), while Maverick is in a critical training stage.
distances are like men. never grab the first one you see; it's never the best one, more will come along.