For preparation:

If you didn't spend time leveling up at the Highbridge, then you will likely have a more difficult time. Best thing is make sure you level up enough until Tidus learns Hastega so fewer turns will be wasted in hasting allies during the battle. Have Yuna's Aeons' Overdrives filled pre-battle as well as their O/D's will help you out.

You should have Zombie Ward armor. An alternative is Auto-Med armor so that Holy Waters are automatically used, but that armor is harder to make. He uses lance of atrophy which inflicts zombie status. He then follows up with Full-Life which can OHKO that ally. You can make Zombie Ward armor with 30 Holy Waters. There's no need to waste turns manually using Holy Waters. Speed is the key in winning the battle.

An important thing is to silence him at the beginning so he can't use Dispel on everybody. Dispel becomes a pain because you will then have to recast your buffs. Rikku should begin the fight with a Silence Grenade for this. Then have Lulu poison him w/ Bio spell or have Rikku use a Poison Fang to do it.