I would generally use Outbreak, to apply both diseases.
That increases the damage on Obliterate.
And Frost Strike is the runic power dump.



For AoE, it is Howling Blast based.
A priority setup, not a two-step.
Press - Howling Blast.
Release - Howling Blast, Frost Strike, Plague Strike, and Death Coil.

Haven't bothered with Necrotic Strike, since they changed it from an Unholy Rune to a Death Rune.
In PvP, it might be worthwhile to work Necrotic Strike into the rotation...
I'm basically just boosting at the moment.