I think the most useful advice for your level is to have (at least) one character with 1 point in hydrosophist, as aguds pointed at, and take the healing spell. You can use it to heal back all your characters once out of combat (but it takes time too because of the cooldown).
A second point in hydrosophist lets you take another healing spell, Water of Life, which xiery pointed at. This speeds up regeneration outside of combat (and in combat aswell, so you will be less likely to die).
Note that better than to heal (and resurrect people) is to not let them take damage in the first place. Controlling ennemies is very effective in this game (as they do no damage and they get killed down faster).
