No one can add anything to the horse that is not there, neither an inch nor a centimeter. Careless will not become a champion. But you can deduct what bothers the horse. Stiffness, dissociation, lack of confidence, lack of balance. Each horse can be developed to the level of its potential.
The best thing is ground jumping on a long rope. He will gain independence and his own techinque.
Also if you have a heave pole you can use and he hits the jumps often, you just repeat the jump until he clears it well and you stop him right after and give him a break as a reward. Every time he puts effort you stop him. He will learn that if he tries harder you will let him rest.
Lots and lots of grids/gymnastics! one is bounce, one stride, bounce.. the other best to use is one stride, two stride, bounce, bounce.
Doing exercises with cavalettis and with ground poles that determinates the strides of the horse could help your horse be more careful and more athletic.
Use wood poles. They hurt a bit when the horse hits them so he learns "ouch! That's not fun! I'm not going to hit it again!" Use poles on the ground to teach him to pick up his legs also
There are two exercises that I know of that can help. The first one is just setting up low cavalettis and having your horse walk through them. It makes your horse think and be careful with their foot placement. They may knock a couple of them down, but as you practice it consistently, they will improve and become more careful. The second one is you set up an oxer or a vertical and lean two poles up against the jump as shown in this picture https://www.pinterest.com/pin/446560119274128609/ . It will make them jump higher and tuck their knees better. Lastly I would suggest gymnastics. Any gymnastic should help. Hope my advice helps!
Well there are definitely horses that are born with a natural ability to jump I believe just as people are born natural to be athletic or artistic but I think you can definitely still train a horse to jump who doesn't have the natural ability. It just might take a little bit of more work.
I was just thinking about this, and I wondered if there was a way horses are trained to be more careful jumpers or if it is something a horse kind of either is or isn't.