Go for warriors in 1 row, archers in 2, bombers in 3, mage in 4 and monk in 5 row.
Always have the highest upgrade unit avaible to you as it can be 3x stronger. So it can easily be an advance to sell out 6 old to buy 2 new upgraded.
Go for the best spell protection in first round as it then will be avaible once more in one of the last round.
an item shop with a few very expensive, rare gems would be nice.
cause money become irrelevent fast in this game.
or maybe if there be a way to buy gem xp