Try travelling to Mysidia via Chocobo, and buy as many of the high-powered weapons and spells that you can afford. Even at the time of entering the Warship the equipment you can purchase in Mysidia is a big improvement on the gear you'll have at that point of the game. You can then lower the challenge of the game greatly.

As well as what rubah mentioned, you can also cast HEAL on an unaffected party member for a +1 increase.