Sit quietly. What I mean by that is to sit relaxed. You want to focus the most in your hips. Your hips should be level with your legs, basically the same as a walk or trot. You want your hips to move forward and back almost rocking-chair like. Feel the horse. Don't think about it, let go of "i should be doing _______ " in your head. Just let your body feel the motion. If it is choppy feeling, you need to ask for more of longer stride from your horse. If you feel like you are going to fast, slow down. Let the horse carry YOU. You are just along for the ride. Keep your hands up and still and relax your elbows. Your hands/arms should move forward and back with the motion of the horse. The horse will natrally pull his head and neck forward and back to carry the momentum of faster gaits. You want to move your hands with him. Being to still causes it to be hard on the horse and to loose causes them to do their own thing (speed up, cut corners, etc).
While all horses have the same gaits ( w/t/c/g) they def do NOT all feel the same. I've ridden horses who have a canter that feels like a rocking chair, some that feel choppy, and some that are so smooth it is just way to easy to sit still and ride. You may just have to get used to your horse's movements as they are all very different depending on the breed. Sometimes even then it will vary between horses. (For example I rode a TB who had the most uncomfortable trot you can imagine. I thought I was going to bounce right out of the saddle. I've never worked so hard in my life to post. It was easier NOT to post then to do it. and this was a former racehorse, pure tb. Then I get on my trainer's TB who is also an x racehorse and he is pretty smooth. Same breed, very different feels).
~He knows when you're happy
~He knows when you're comfortable
~And he always knows when you have carrots.