When you are in the EXP Dungeon there is a button in the upper side of the screen, which says Encourage. Tap on that and it will give you the option to select Gold Inspire which will give you more EXP! I suggest that you do this every time you do the EXP dungeon, which you should do daily. It will help give you a huge boost of EXP, so it's definitely worth doing it ASAP because it will let you equip better gears and thus let you become stronger.