I used to spend heavy cav like it was monopoly money. As a catholic faction it's easy to do because later in the game you simply outclass your opponents. Now I try a combination of tactics based entirely off of the strengths of the available troops of the faction I am playing. For instance, when playing the Byz, head on is the way to go. Kataphractoi are murderous head on and their only real weakness is against mobile missile troops. VGs can shred any force, but if you can't catch em, you can't kill em.

With the Turks, until you get JHI, you need to dance around your opponents and you don't charge until your foe is about to break or is actually fleeing. As for Futuwa, keep em in the treelines and reign death on your opponents. If they have horse or spear and send them after you, withdraw into the woods and make your stand there. If they send sword or axe infantry, skirmish with bows. I use some interesting indirect tactics when playing lighter forces like the Turks.

I like the English though. As a faction, you get one of the most lethal combinations of troops in the same year, still fairly early in the game. It is the only faction I have played so far that I can field an entire force without any cavalry and still win consistantly. That said, combining them with steepe light cav is a lethal combo as the fast cav is fantastic for chasing down withdrawing/routing enemies. Enemies can't stand off and kill your troops with missile fire as your longbowmen simply outclass any other missile troops and if the enemy closes, they will suffer from missile fire before they reach your formidable billmen wall. When they run, you chase em off with the light cav. Hobilars and Mounted Sergants are OK, but not as fast as the boys from the steepes.