If your horse has never been ridden english before I would take the transition slow. Lunge him with the saddle first. And when you ride him go easy and let him get used to the different movements. Another thing that helped for me when I transitioned one of my horses was to ride in an english saddle and bridle but use a longer more "western" rein and slowly let him get used of contact. If you horse has never has contact and you just hop on him and hold your reins tight, he is not going to be happy.