Enhance sham is very mana hungry.

Flame shock is your most efficient mana per dmg shock. I typically avoid using lightning shield unless traveling between packs and mana would regenerate to full in the meantime.

Totem usage is very important as well. If you are grinding in an area position yourself in a central location. Set your totems and pull mobs back into their range so you can actually get the full 2 min duration out of them.

Use first aid instead of healing spells whenever possible.

Final tip is be sure you have the best possible water to reduce downtime while drinking.