When attacking loose-order low-quality infantry with heavy cavalry I've often found it useful to order the horsemen move through the enemy unit after they've charged, and once they've penetrated deeply into the ranks tell them to attack; tends to result in a real massacre and a wholesale rout in a very short order.

Work with heavy infantry too mind you, or about anything else that has the mass to push into the enemy ranks that is actually able to out-fight its opponent too...