It is really essential to have a strong core and legs to be able to lift yourself up with the horses motion while still keeping your body tall so you don't collapse on the horses neck.
For me, counting my strides, sitting up tall, finding a specific place Beyond the jump, and really pulling my shoulders back😊
Jumping and schooling for a month with out stirrups did me the 🌎 of good - it was extremely painful but never had a problem with my position again
Carry your weight in your heel...imagine your heels as your heaviest part, all your weight falls down the back of your leg and absorbs into your heel. And of course, dropping your stirrups does wonders!
stiruppless work and bareback helped me in so many ways...it’s not even funny!
Try and hold your hands straight on their neck and push your butt back and let them jump up to you, squeeze with your lower leg and knee
For me doing tons of stirrupless work helped a lot. On the flat and over fences