My advice would be to utilize Shroud (MP regen effect if I recall) and to focus on mana efficinecy. Every time you over-heal, you are basically wasting mana away. Larger heals will take a lot more MP to achieve less of a result then say 2 heals of a lower level heal. Its all about balancing out your mana usage and limiting your large MP drains for emergencies and minimizing the over-healing you do.