I read somewhere that you need to try and push your horse forward and then recycle some energy through the reins to transfer it to the back and gain impulsion. Is that correct? I've been trying to do that (trying), not necessarily doing it properly I suppose, as when I look at videos of me riding my school horse I feel he's lacking a bit of impulsion. It's not horrible, sometimes it's actually quite good, but at other times it's really not ideal. (I can post videos if need be).
Also, how can I get him to round his back?