Go to the forest outside of Meedeel and walk around until you fight Head Hunters or Caterpillers. Equip Cloud with an Apocalipse sword and everyone else with a Rune Armlet. If you fight a group of four Head Hunters, you get 340 AP. Caterpillers and a group of three Head Hunters give you 240 AP. Equip as many 'ALL' and 'MAGIC PLUS' materia a possible in the sword and Rune Armlet. When mastered, they are worth 1.4 million gil each.