Sit deep in your saddle and push your knees and heels down and if he's going to fast try tightening your reins and sitting back in the saddle. Hope this helps x
Sit deep in the saddle and lean back slightly. Let your hips move with the horse loosely, but not too freely as to the point where you are out of control. I hope this helped
Try asking for the canter at a sitting Troy
What helped me was every time they lead with their leading leg, imagine pushing your heel down and putting you belly button to their ears which will help you sit back.