You first have to unlock expert difficulty by completing the game on either normal or advanced difficulty. I recommend you play on normal difficulty and then play on expert difficulty which will unlock the advanced difficulty achievement as well. Expert difficulty isn't that hard and can be completed really quickly. I recommend you use the Impedimenta spell throughout the campaign. With this spell all you have to do is mark enemies and then cast it and it will kill all the enemies you have marked in one hit. Use cover often and don't be afraid to backtrack so you don't get surrounded by enemies. Also leave the collecting for your first playthrough so you can just run through this playthrough quickly. All the spells you unlocked on your first playthrough are available to use from the start of your next one.