I had only 4 for the longest of times:

Self / Protect
Ally HP < 10% / Phoenix Down
Foe: party leader's target / Horology (or numerology)
Foe: targeting self / Attack

Then I added a combo for too many fiends:
Foe: targeting ally / Oil
Foe: status = Oil / Flame

Then I added "Drain" after I got the spell. And "Syphon". And "1,000 needles" for the undead. And....

Now I use all 12 for each player