Best Tip I can give you for beating dungeons is use health potions and health food when dying, using mana potions and mana food when low on mana and needing 200 to 300 mana for bosses and to clear the room with a big traveling skill, and to always press ctrl for more attack before fighting the last boss.
always repair your gear at a shop or armor shop to keep doing highest amount of damage, upgrade to better title that gives more critical/maximize/or adaptation stats as you level up, most important stats on weapons and armor is critical, maximize, and adaptation. Important skill upgrades just click the up arrows next to the skills to upgrade them, always choose upgrades that say (ignores armor) or (lasts longer) or (every attack is critical) . skills you want to be choosing are all the newest skills you get from the bottom up like the highest level skills unlocked, drag and drop those into your hot-bar at the bottom of your screen, they are more powerful and are unique to the class you chose. and before you start your dungeons always teleport to a hot spring with the wing icon at bottom right, go to the water, and wait until the countdown is done. that will give you 30% exp more for 29 minutes of game play. always press ctrl for attack buff right before fighting bosses, this should help you a lot!