Indeed solid cavalry charges are very difficult to pull off. As they should be, because the barded+ horses can decimate even the heaviest infantry in an instant. They were also historically difficult to pull off. As one turkish general put it, waiting and maneuvering for the perfect cavalry charge means certain defeat.

You need flat, open space for a solid charge. Need at least 3 units space away. Though the more the better I prefer at least 200 yards. For a more devastating charge, first start your cavalry moving (not attacking) towards the enemy at a normal march pace. Then after they are moving and have organized themselves again into a straight line, double click on the enemy. This will cause a full speed, well disciplined charge. With the heavier horses they can decimate multiple units at once.

Important, maneuvering careful double clicking when a unit is stationary will cause the cavalry to become disorganized. Also be careful, waiting for the perfect area for a cavalry charge usually means putting yourself in a disadvantageous position.