It's all about knowing the incoming damage and read your party. Even in DF groups it's possible. I hardly ever have mana issues even with groups that are not really ready for AK dps wise.
One thing that you need to get a feel for is if the whole group takes damage do you really need to cast a Medica II or is it ok to throw regen on the additional party members. Most AoE comes in waves and is predictable.

Also, as the others have mentioned: I never use Cure III, ever..I think I cast it once to try it out in Ul'Daahl..on myself

Cure I carries you nicely through everything trash with the odd Cure 2 thrown in on procs.
Stoneskin is nice to get a bit of buffer before a fight and using Virus on a boss or hard hitting mob can also lower pressure on your MP

Use SoS early on so you have it available again as soon as possible if you know you might get into trouble.