If fire don't work try every others and if it's still not budging it's just magic immune and you go melee if it's still too hard well run away and try again once you are stronger.
@Kamelpov I agree with your process of elimination.
Kinda wondering though if they could "compress" spells. I mean like increasing the temperature of a fire ball, making stone bullets and ice lances denser, or upping the voltage of a lightning bolt. Maybe some creative stuff like guiding the fireball into the nose, mouth and or eyes.
@Armsdealer12 , I suspect that doing that is one of the key skills needed to increase rank, as compressing power means you can use your magic more effectively.
@Armsdealer12 creative way require modern chemistry knowledge. Like making high oxygen concentration around the target or making the lung explode with air pressure. And stone bullet are basic spell you need to add speed and rotation and the shape of a cone so it's way more difficult. Also you can go powder explosion with small particle and ignite the whole like in some manga they throw enough flour and make it explode with the right mix with ambient air.