I guess it's kind of army composition but just wanted to focus on cavalry and see what the approach of others is.

Firstly leaving aside all-cavalry nomad style armies - assuming the army has some kind of infantry line. Also this is for later game full stack or near full stack armies, for lesser armies I just go with a similar proportion. I have 19-unit 'full stacks' due to the convenience of merging, I personally never retrain anything except garrison.

For what I consider 'cavalry-heavy' factions e.g. Pahlava, Hayastan, post-reform Saka etc., I like to use 6 units - two cataphracts, 4 medium lancers. For nomadic or ex-nomadic factions I also throw in 2 horse archers.

For 'normal' factions with a tradition of using good cavalry but not necessarily en masse, e.g. Macedon, successors, Carthage, I use 4 units, generally two heavy and two light.

For 'infantry-heavy' factions, Rome and KH, I usually use two units of whatever I can pick up and use them defensively or to chase routers. I try to avoid too much hammer and anvil tactics as factions who didn't really fight that way.

Obviously these aren't hard rules, just what I generally aim for. What's your approach?