For cavalry I think that the best thing is to charge with your light horses at the flank of the enemy and then use your heavier ones to attack them from behind.
Light cavalry will most probably take some heavy losses but they are usually cheaper and easier to retrain than heavier ones. Some people might desagree but I think that light mail upgrade for hobilars/ border horses make them last a while longer while your heavy cavalry charge from behind and annihilate/rout those Heavy Swordmen bastards, even though they have a strong defence, they are usually no match for a well organized attack.

If by some insane reason you have to charge an enemy spearmen unit, charge first with your light cavalry in column formation and then use any heavy cavalry to flank/rear them in line formation.
That tactic always work well for me even when outnumbered.

For some strange reason, enemy troops don't like cavalry charging against them...