If your horse lands on the incorrect lead after the jump, half halt, Balance the horse then shift your hips and switch your legs. Point the horses nose in the proper direction (slightly) and give and small kick cueing for the new lead. If the horse is well schooled they should change without problem.
What I was taught was when jumping, look in the direction of my next jump (so if I was turning right after the jump, I'd look right) and to put my right hand slightly more forward if I were turning right. It's great practice to do a course that has several reign changes, eventually your horse will get it