This is what i do. (and i always wait till i'm at lvl 99 so don't feel bad)
Conserve your MP for curaga and don't use potions unless you really need them.
He always uses his one attack that you have to block after Heartless angel so don't cure yourself because you won't have time.
When he sends out those black thingies just start whacking them
Make sure you have abilities like second chance, mp hastega, aerial recovery, and retaliating slash
i've also noticed that he likes to use heartless angel when you're really low on HP so try not to use too many potions then.

You best bet is to memorize his pattern and then go from there.