How can we develop real fencing skills on horseback? As on foot, practicing both ways.
First, get used to swing a wooden practice weapon while riding.
Then cut with a real saber on targets. Fortunately we know the mamluk excercise: stick a reed as high as yourself in the ground. Approach it in gallop and cut away a span of it. Repeat it, until you cut the reed knee-height. If you can do it, place more and more reeds in a row, then put them both on your left and right side to be more and more precise and fast.
Of course start every excercise slowly, but when you are ready, always practice at full speed.
As a British cavalry manual states, they didn’t teach blocking, because speed is your best defense. It is not working to swing your sword on a standing horse, especially against infantry. Whatever you see in movies, in my opinion a footman is superior to a standing horseman. Even though the horseman is in higher position, he is bound to his horse, cannot move so quickly. The mamluk manuals confirm my theory, if a horseman looses speed and get stuck among the enemy, the game is over. I write down theese things here, because the shorter your weapon the faster you have to ride to survive. You can shoot from a standing horse, you can slow down to maneuver with a long spear, but you cannot really defend your legs and your mount with a short saber.
So neither walk nor trot your horse but push it hard, when you simulate battle.
There is an other good target described in the abovementioned British manual. It is a counter-balanced dummy, which „stands up” after you strike it. I will make a plan of it soon.
Second, use sparring weapons against other horsemen or footmen. You will notice that it was a really good advice to start your riding career with mounted wrestling.;)