Well first i would regem towards strength. then i would hit up heroics so you can save up some justice points to use towards armor.
At this time your rotation should be focusing mainly on keeping your Blood plague and Frost Fever up. Using Pest to spread them to nearby foes as well as festering strike to increase duration of your plagues.
When ever you are able to i would use Death Coil to use up some of your runic power. anytime your maxed out on runic power without useing something to deplete it your hurting your dps.
I would also toss in bloodstrike obliterate and scourge strike whenever possible.
DK dps is not necessarily a rotation but more of a list of priorities.
Another thing haveing at least 21expertise is a must if you want to actually hit something rather than miss it all the time. 26 recommended but 21 at least.
Also switch your weapon enchants from cinder to fallen crusader. this will help alot.
