Pretty straightforward. How can you guarantee a high roll on Divine Spell Power (Complete Divine feat)? For reference, you need a 22 on a turning check to get the +4.
So far I know of...
Boosting your Cha (duh)
Circlet of Persuasion (+3)
Knowledge Religion 5 ranks (+2)
Glory Domain (+2)
True Holy Symbol (+2) (Planar Handbook)
Hallow (situationally, of course, but when you're on Hallowed ground you get a +4)
That at least guarantees you'll get a +0 and makes it fairly easy to get the +4, and doesn't cost too much (THS: 500g, Circlet: 4500g). Even if you didn't invest in the Glory Domain, you've got a +10 bonus to the check before Charisma. However, I'm wondering if there's anything I'm missing. After all, I've been away from the CO game for a coupla years now, I could be rusty.
What else could push these rolls higher?
Edit:
-Action points and rerolls help with any d20 rolls, of course.
-The Luckstone, Pale Green Ioun Stone, Admiral's Bicorne and Breastplate of Command help too, but they're pretty darned expensive. What can we do to get the bonus up there faster?
-Heighten Turning and Divine Energy Focus, but I'd only recommend it if you want to boost turning for other purposes too, since a cleric's feats are precious.