Bosses
Unless there are monsters around the Boss that can be targeted with Deathblow, immediately take down the Boss with everything you have. The goal is to kill it before it moves. You can handle the smaller threats later.
Healing
It takes longer to heal without bandages or food, but this should be done in dungeons with where the end is far away. Unless they are in danger of dying after a battle, keep ending turn after turn and use the mage to heal everybody for free.