The first thing you should do when you arrive at a new dungeon is look for a save point. When you visit a save point, your character HP and AP are refilled when you come within range, even if you don't access the save point from a menu. This handy fact means that you can create powerful elemental abilities to counter the local enemies, then use those abilities at the start of each battle. Then, once you win, you can immediately restore your characters at the save point and repeat the process for the next enemy group. This allows you to more quickly clear enemy groups and gain levels.