Well, ride with the horse, when I lope my horse, I moved with his body instead of against. If you move against, you'll end up with your butt in the dirt, and horse in the feild. Lawl. But remember to have fun with it :)
Well my suggestion would be if you have access to one, use a bareback pad. Of course one without stirupps would be better, but otherwise just keep your feet out of the stirrups. It's just something to grab onto if your horse goes a little willy-nilly with it's gaits. But as others said, definitely practice the canter with a saddle and perfect the gaits. Then once that is good and you are confident you can move onto perhaps a bareback pad, then once you can sit through that move onto true bareback. Another thing is perhaps holding onto the horse's mane.
When I was riding at my friends house I didn't have much confidence because I hadn't ridden her horses in a while. We always ride bareback, but I put a bareback pad so I would have something to hold onto. By the end of the night I was sick of it and took it off. It didn't take much for me to then remember to grab onto the mane and I was absolutely fine for the rest of the night. The next morning I was just as confident and didn't even fall on my bum once! Such a contradiction to my username. [Perhaps I should be on a starburst commercial. /fail]