To begin, you need to do a lot of flatwork. Work a lot on ground poles and cavalettis. I personally realized that I was less and less frequently jumping high. The most important is to work with precision and above all practice. In order for it to become automatic. That’s not because we put higher jumps that the horse will slow down. If you’re able to do it on 30, 50 cm, you’ll be able to do it on higher jumps.
Don’t hesitate to take some time off if you can see that you’re asking too much and try again the day after.