I spent all my free diamonds on increasing my inventory space. Then I play the spinning wheel mini game daily to earn 10 diamonds each time. The 10 diamonds reward is always on the first slot. If it doesn't appear, try going back and re-enter the spinning wheel mini game until it appear or you want other better reward like elixirs. I also earn some diamonds from arena just to spent it all to buy a ring.

Alas, I uninstalled this game 2 days ago because I don't have the patience to wait around for my gears to be leveled up, runes to be combined or removed. The dumb inventory space is way too small for me to hoard any gears/runes around to upgrade them or remove slotted runes to sell them off. And I cannot even select which slotted runes I want to remove, it automatically remove all the slotted runes costing me tons of gold coins and inventory space which is the last straw for me. Otherwise, it could have been a fun game.