One of my favorite jumping exercises is setting a verticle with some trot poles before it. It is great with helping the horse round over out fence and helps the rider with their position over trot fences. As you raise the verticle, you feel the horse round out by lift their back, stretch their neck, and tucking their legs. It's great for young horses to help them developed their jump.
Not sure whether you do hunter, jumper, xc, or something else, but cavaletti exercises are always good, grids, using trot poles in front of jumps, trot/canter poles by themselves, working on related distances, or ditches are my reccomendations!