Thankyou everyone will definitely try it next time I ride :D
Think up and grab the mane
Pretend to reach for their ears or grab mane
You can hold on to the mane
You can spray horse safe paint or twinkle toes where you want to put your hands that way you can clearly see where your hands should be.
My old instructor put a stirrup leather round the horses neck at where my hands should go when I jump as a sort of marker. It really helped and worked well :)
Grab mane to begin with, that way your hands can't really move down. After your hands get used to staying in that position, you should no longer need to hold onto mane