I know I've probably asked similar questions in the past but it takes a few explanations for some things to sink in with me.

I've gotten my drk to lvl 70 and have been doing okay so far. But I noticed that with the higher end dungeons I struggle with damage mitigation. I know I need to use my heavy cds first and lighter ones second but I'm trying to work out which one is the best and if I should pair any in different situations.