Well it depends on your spec. My DK is Frost and he does something like

Single Target

Icy Touch, Plague Strike, Blood Strike, Blood Strike, Obliterate while spamming all his trinkets, cooldowns etc

AOE

D&D, Icy Touch, Plague Strike, Pestilence, Howling Blast, Blood Boil, Icy Touch Plague Strike, Pestilence, Howling Blast while spamming all his trinkets, cooldowns etc

I am sure there is better but that is what I use my DK is really set up as a meat shield and he does 1100 DPS on average. He has mainly AH bought epics and quest blues.