Each hero has its own powers and weaknesses. Use that to adjust your attacking style. Melee fighters are usually better than the ranged ones; try to tip the balance over to that type. Consider starting with two archers then summon as many melee troops as possible. Delay the start of the attack for as long as possible. The closer you are to your starting zone, the faster the summoned troops will arrive. Regularly call in reinforcements to replace your lost troops as fast as possible.