Well you kind of need to win first attack because usually your units will be surrounded and take more damage.You need to focus right away on some kind of weapons and what i do is aim for the forget their name but the melee that can attack 3 squares.Then with that i pair up with cavalry as they can go through the line so with two guys you hit all 3 twice.

"Mana"you use mana everytime you do upgrads which imo is kind of lame but whatever,use your upgrades wisely.I was using armor the first time i played but i don't use it anymore ,waste of mana.Upgrade things like the counterattack or dmg and if doing the poison one stack several on same guy.

The actual accuracy in game imo seems bugged because you can't rely on ranged attackers when game tells you 95% because 95% misses a LOT,too much to be legit.

You shouldn't need to cast magic that often,sometimes the aoe scrolls will deff be needed and help but try and save them for when you really need them.

Last hint/clue:Don't waste your resources as a few are must haves to be able to craft weapons.So be careful what you are using when crafting and again remember that adding those upgrades costs mana..too much mana.