Perishable pretty much said it all. High HP and the ability to take high damage/spam yggs is all you really need
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Reduct items such as Poring Tower Hat, Sacred/Fluffy Wings, Skull aura, or even just Ifrit rings can really make a big difference since you'll be taking less damage. Cards such as strip cards, decrease agi and dispell are also useful, so you can further aid the person you are devoting.
When you're devo-ing someone, make sure to always re-devo them. The devotion effect wears off pretty easily.