It is common knowledge that death knights are more squishy by nature than our warrior and paladin counterparts. The trick is, how to counter-balance it; which we can do to a length, through game mechanics but it is always going to hurt us and I figured it would serve well to right down something on the subject, to all those of us who, at times, struggle to live up to our peers.
Some of us remember the happy days, before the huge load of death knight nerfs that literally killed our health. I am not saying many of those nerfs were not warranted, but I said it then, and stand by my argument that there were too many cutbacks. From the start of the Wrath, death knights lacked shields, therefore the developers gave us higher health to balance it.
Now, we are on par with warriors and paladins, overpowered as they are, can even go beyond us when properly specced. So what can we do about it?
At this point I will ensure that you have a proper specc and at least moderate gear, concerning the level of content you are playing, and skip those parts. If you think you lack in these areas, have a look at Ensidia’s death knight tanking guide for 3.3. I had a look and it is really good and thorough.
I would bring attention to one piece of gear though, which is your sigil. It is very important that you use the right one. Right now, my personal choice is the sigil of insolence. I went by a dps sigil during ToC, for threat purposes, but now in ICC, insolence is the best.
Another piece that should belong in your inventory are potions; specifically Indestructible Potions. On my server they are very cheap and you should carry a truckload of them. In ICC in particular, even on trash because everything in that place hits rather hard. Pop one right before you enter combat to start the cooldown, and if the fight (doubtful with trash) lasts longer than that, pop another after it expires. Same goes for bosses and generally you will need to use two for every boss kill.
Next are your cooldowns, particularly as Frost or Unholy, you have the choice of Unbreakable Armor and Bone Shield, both which also help your initial aggro. I have personally noticed that before the first hit lands on the tank, healers can primarily only wait. So by reducing the damage that the first big hits deal, you are prolonging your life-expectancy.
Next comes Antimagic Shell, one of the cooldowns you are using near constantly in ICC and it never hurts to use it elsewhere either. The good thing is that when to use it, is also easily predictable because it usually involves casting, effects landing from the sky, or breath weapons. Magic damage is simply everywhere, and not only does it heavily mitigate the damage, it provides you with oodles of runic power.
Last I’ll bring attention to avoidance. While it is true that effective health outranks avoidance, little bit of extra cannot hurt, from wherever you can get it. I am still using the Heart of Iron trinket, thanks to the avoidance boost. You can also gem for dodge/stamina in gear, if the socket bonus supports it. A general rule is that if the socket bonus provides +9 stamina, you can go for it. Anything less is a waste.