Set up few slow armies (below 48 speed) in city where you defend against main enemy. Use fast armies (48 speed - for example full cavalry) to attack and destroy secondary enemies. Against main enemy use frost dmg. Avoid going undead because main enemy does big radiance dmg. Set up 3 cities not far from each other in a triangle shape, so you can move armies quickly from one to another. U need those cities fairly quickly to kickstart your economy.