This is a guide for Death knight dps, the current patch is 3.2.2 so this specc is relevant for here and now :). I've played all three speccs in Pve and even though the other two speccs are fun, blood specc is clearly the most damage output.
First of all you will want to reach the Pve hit cap which is 8%, this will make sure you don't miss any special attacks such as Heart Strike and Death Strike. (Hit cap under 8% will result in a serious loss of DPS)
(PS:PlagueStrike, IT: Icy Touch, HS: Heart Strike, DS: Death Strike, DC: Death Coil)
PS-IT - HS - HS - DS - DC -> DS- HS - HS - HS - HS - Repeat
Tip 1: Keep above 25runic power at all times, this will ensure your Death Strike hits as hard as possible. (Death Strike scales with Runic power when glyphed)
Tip 2: Keep Plague Strike and Icy Touch on the target, it significantly increases your dps.
Tip 3: Spam Death coil when your runes are refreshing.
Tip 4: Dancing Rune Wepon as much as possible, try to refresh diseases after you summon it to increase damage, it is also a good idea to use Hysteria before summoning it.
Note there is 4 points spare that you can put into what you want in the blood tree, I have chosen Bloodworms and Vampiric Blood because you do more damage when over 75% health (Bloodworms help) and VB helps tricky situations + viable tanking offspecc.
Glyph of Death Strike
Glyph of Dancing Rune Wepon
Glyph of Dark Death
Any questions on this specc send me a poke :)