depends on what your doing, just questing I use a seal of wisdom ( and if you don't have shaman dropping mana totems blessing of wisdom too )
but for a heroic dungeon I tend to use seal of vengeance more ofthen that wisdom because it generates more thread, that and retrobution aura.

try to keep divine plea & holy shield up over other stuff, the more beating on your pally the better for your sanctuary to give mana.
/castrandom holy shield, divine plea,
/castrandom xxx,yyy,zzz