1) Have every Upgrade possible
2) Use following Potions:
-Flask of Security (Because one extra lock per chest isnt that hard - for 15% more score)
-Potion of Invulnerability (The more shield the better)
-Potion of Holdfast (15% more score for 30% stronger enemy hits. the enemys should die very fast, so you wont feel the 30% more, but the 15% more score!)
(For this achievemeent Potion of Holdfast is very nice, because enemys die very fast. But if you struggle with killing, than take it out.)