Majority of your ”durability” comes from your self healing and using Death Strike at the right time. Death Strike is not spammable like it used to be. You will want to use it only after receiving a ton of damage. You also can’t use Death Strike preemptively, because the healing comes from damage already received in the past few seconds. (Sorry don’t remember the exact time window. Maybe 6-8 seconds).
And you will want to help sustain yourself with defensive cooldowns outside of those windows of Death Striking. In PvP it definitely takes some getting used to. It will take practice and getting better at understanding which cooldowns to rotate through.
#1 mistake I see, and I myself also make, is holding onto Vampiric Blood and not using it enough. With all the talents, this defensive has a quick cool down. So be sure to use it often. It will account for a ton of your survivability and healing. Get into the habit of pushing it. Like at least 20-30 times or more.
Your main defensives are Vampiric Blood, Rune Tap, AMS, Blood Shield (from Death Strike), and Tombstone (if talented). Use them often.
Generic but things to think about to help for surviving.
-Keep chains of ice up.
-Keep Bone Shield charges up.
-Save a grip for when enemy tries to kite, incase you need a guaranteed Death Strike to land. I usually will grip classes that can’t easily kite me such as Priests or Locks and sometimes pets if needed.
-If talented, your AMS will heal for 100% of its absorb value. So use it as damage mitigation + healing against casters. AMS can also be used to immune yourself against magic CC. Also if talented, AMS will have a short cool down.
-If talented, you can use AMZ against magic as well to mitigate magic damage.
-You can use chains of ice to slow melee and try to evade some of their burst.
-If talented, Death Strike will also provide reduced physical damage taken for 3 secs.
-Use Icebound Fortitude to break out of Stun and/or prevent incoming stun(s).
-Save your runic power for Death Strikes
-With all talents, Dancing Rune Weapon summons 2 weapons, generates 5 Bone Shield charges, helps quickly generate runic power from Heart Striking, and has a very short cooldown.
-Be sure to have Death and Decay down, so Heart Strike will hit multiple enemies and help generate more runic power.
-Blood Tap is a talent that is helpful as well allowing you to instantly restore runes. Has 2 charges.
-Dancing Rune Weapon and Blood Tap both gain cooldown reduction from Bone Shield charges being consumed.
-Disarm really hinders Blood DK. Having Death Pact talent or Sacrificial Pact (requires Ghoul pet) can be an emergency heal in these moments.
There’s more that can be said, but much of it is understanding the Blood DK class and its talents. There are additional talents that can be taken for more survivability. But hope this offers some additional clarity.