Keep your heels down sit deep like Hailey said sit on your pockets not on your tail bone don't "perch" as the saying goes shoulders of a queen hips like a whore. Feel the ride don't work against the horse become one!
Sit deep and push your heels down and legs a little forward
Maybe over exaggerate your hip movement for a while. Sit extremely deep and practice pushing the horse using your seat for a while. Eventually, it will become so natural you won't have to exaggerate so much. Make sure your legs stay in place and your feet/weight are planted evenly in the stirrups. Good luck! :)