While it can be useful in some situations to ride along the rail, fence, or wall - spending lots of time on the rail can actually be a detriment to your training. Why? Because the rail can act like a crutch. It can hold your horse on a straight line when he is in fact not straight at all.
Horses need to be honestly connected and on the aids before they can stretch properly over their entire topline. Without that connection from behind, the stretch will be the horse's neck only, which is far less productive than a real stretch over the back.
In the sport of Eventing, ensuring that our horses are truly fit for our level of competition is one of the best ways to prevent unnecessary injuries.
Always use both reins together to steer, especially when jumping. Using one rein only turns the horse's nose - but using both reins turn the horse at the shoulders, which means his body will more accurately follow your chosen line.
"Contact doesn't only refer to the hands, reins, and bit, but to the whole rider. A rider must give the horse contact through his entire seat. This means that his legs must lay gently against the horse's body, his seat must be balanced and supple,