I'm still trying to figure out the optimal way to play DRK, but if I had to give a one tip, it would be to make full use of how often you can use DA + Dark Dance. Yeah, the evasion goes against a few DRK skills, but mitigation is mitigation when you have a lot of incoming damage. As for the other cooldowns, throw them on during Dark Dance's down time and/or when there's a big hit coming.