I just found this on arena junkies and found it HUGELY informative. If you play dk, especially with 4.06 coming and possibly switching to unholy, this will be an amazing read for you imo.

link:
http://www.arenajunkies.com/showthread.php?t=224560

Here's some highlights i didn't know but you really should read this...

In the starting areas of BGs/Arenas, stack 5x Shadow Infusion on your ghoul to be able to transform it right out of the gate. Death Coil costs no runic power during arena preparation.

 Although Cloak of Shadows causes Chains of Ice to resist, Outbreak goes through it. So if you don't want the rogue to vanish, immediately use Outbreak soon as he pops Cloak of Shadows.

 Dark Command has a chance to proc Unholy Strength.

If anyone has any other tips they use feel free to throw them down.