Auto-Life for all, multiple status-guarding abilities for all (having a high Spirit stat also helps avoid bad statuses). Equip everyone with Shadow absorbing/guarding items and Holy guarding items, keep everyone off levels divisible by 4 or 5, try to round up as many Phoenix Pinions as you can and put Eiko in the party, since there is a chance Phoenix will revive an annihilated party if Eiko is in it, the odds are (# of Phoenix Pinions / 256) %, um...

Wait until Ozma is attacking before entering your commands, since he can act the second anyone's ATB is filled. You don't want to be in a situation where Ozma is counter-attacking every single command you enter.