Heels down and try takeing your stirrups off
Thanks everybody I will try to apply your tips :)
No stirrups, lunge lessons, and exercises on the ground to strengthen your core :)
What my trainer did was put me on a line in a round pen, made me drop my reins and stirrups. Helped a lot with my seat
A good exercise is to have someone take your horse on the lunge line while you sit on it with no stirrups, so you can focus on your balance and posture.
take you stirrups away for quite a while