Luck and Item Drop cap at 650%. I’m around 500%, and I don’t play much, have gotten a Crystal and Eternal and tons of other legends in about two or three hours of play. Just get maps (buy or farm) at floor 101, play until whenever you want, I use until 200, then restart the cycle. Meanwhile, increase your Luck, Item Drop, and Gold Find. Other than that, pray to RNG 
Also, when you have means to, get a ring with four slots (I just used a rare ring) and put Hunter on it. With the Hunter Ring, shrines will spawn 1-3 epic monsters. If you kill 50 epic monsters, a legend one spawns, and, when you kill 10 legends enemies,a mythic one spawns with a 100% eternal drop rate. Mythics | DungeonQuest Wiki | Fandom
All you have to do is equip it, click shrine, and put your other ring on. 
The set affixes Nadroji, Eternalized, Crystalline, and Adventurer, Also help alot with farming. You can find those in your dictionary in game. 