A few facts that have things to do with mining.
*If you take damage, but don't get crushed, you only get 1 mining exp.
*If you did but find nothing, you get 2 mining exp.
*If you get immediately crushed, you won't get your EXPTNL raised unless you're level 50 or higher (not sure on the number, but I know it's not lvl 1

)
*HP boosting items you might want to get your hands on:
Armor:
Soul Protector (90 HP Mod)
Spirits Guard (75 HP Mod)
Weapons:
Dragon's Tooth (80 HP Mod)
Demon's Tooth (65 HP Mod)
*Between Mining Spells
Healing Spirit: 150 HP healed for 30 MP (Water Lv 14)
Godly Force: 900 HP healed for 125 MP (Holy Lv 46)