When invading an enemy territory, make sure you start with a Saddle, Orb, Peacock Amulet, Tiger Amulet, Tortise Amulet, Dragon Amulet, as well as Serpent or Naga Earrings if available. Go directly to the enemy's main camp and kill as many of them as possible. It is possible to get 3000 KOs per level. When you have the earrings equipped you can get max stats quickly because you will get +2 attack and defense for every 100 kills.