I agree with developing valor provinces straight o master of the appropriate type ecspecially good with cavalry bonus provinces. But i also try to upgrade quickly in any province i get with iro (metal smith) available so later in game can upgrade those units with higher building specs to give better attack, they usually have good armour from there origional province or building specs. But also keep some provinces producing morale only for the desert.

Also don't always retrain like to join up high valour units to make full high valor units,might retrain left overs or if full unit needs upgrade not just for numbers.

unless really rich then build slaughter build slaughter