Since you're just starting, focusing on the group's hp is good. A good place to practice switching are with fates especially if you can team up with a friend. As you gain more comfort with your spells and timing you'll find your groove and be more confident in what you're doing in the dungeon. As a healer, keeping the team alive is more important than throwing out a spell or 2. That being said, it doesn't hurt to quickly throw an Aero onto the enemy that the group is attacking.

Be patient with yourself and don't be afraid to tell the group at the start of the dungeon that you're new and open to suggestions, a lot of peole are understanding and willing to help.