The most useful place to use this for survivability is when you accidentally stand in the fire, so to speak. For example, when fight the Elder Council, it may be just the ticket to save you from Kazra'jin's lighting trail or the feedback from Overload. It can also be useful for avoiding lightning damage from Jin'rokh the Breaker. Finally, since it prevents the application of magic debuffs, you can often use it to save yourselves from snares or debuffs, if you can anticipate when they'll be cast.
The downside to using Anti-Magic Shell as a survival tool is that it's also technically a DPS tool. Since it provides runic power, it fuels the your Death Coils and Frost Strikes, so in theory, you want to use it any time you're low on runic power and a spell is about to target you. This means you're less likely to have it handy in an emergency. Whether you want the extra runic power, or want to save the cool down for an emergency is ultimately up to you.
The stunning power of Icebound Fortitude
Icebound Fortitude certainly isn't as powerful for DPS as it is for blood tanks, but it's still a lifesaver in the right situation. If Anti-Magic Shell is down, 20% damage reduction when you're stuck in an AoE is better than nothing, and if you accidentally pull aggro, it will reduce damage that Anti-Magic Shell can't touch. In addition, the stun immunity can be very helpful. It won't work on every possible stun, especially on big bosses, but it can be case while you're stunned, so when you have no other recourse, you can get Icebound Fortitude up and hope it helps you ride out the storm.
The talented survivalist
At level 57, you have your choice of 3 talents with the potential to save your life.
Lichborne's great for breaking out of certain types of crowd control, which gives you a chance to use other healing or survival abilities. Even more important, though, is that it gives your Death Coil the power to heal you, so you can spend your runic power for a quick burst of healing.
Anti-Magic Zone is great in that it acts like Anti-Magic Shell for your entire group or raid. It also has the advantage, unlike Lichborne's Death Coil trick, of not taking up resources you could be using to do more damage.
Purgatory allows you cheat death once, but it pretty much relies on you having an on the ball healer or some spare healing power of your own not to immediately due seconds later. This one is probably going to be more useful for the tanks.
At level 60, you'll get another choice of three talents, all of which will give you a pretty sizable boost of healing, all of which have their ups and downs.
Death Pact is one of the easier to use talents on this tier. Since it doesn't take resources, it doesn't require breaking your normal damage rotation as much. The downside here is that you must have an undead minion alive to use it, and it will damage said minion. As unholy, you always have one out, so you can at least use this pretty dependably. As frost, you will have to make sure you save Raise Dead (or Army of the Dead) to use in tandem with this, which can be a bit of a bother if you're saving them for a burst of damage. Still, it's a popular choice since it's the most uncomplicated of the level 60 talents to use and has the least detrimental effect to your DPS.
Death Siphon offers a decent chunk of healing and does some damage to the enemy in the process, but does cost a death rune to use, meaning it will disrupt your damage rotation (frost more so than unholy, which can just slip it in in place of a Scourge Strike). The advantages here are that it's a ranged damage dealer, which means you can use it in cases where a mob is out of reach and you have no other way to do ranged damage with your runes. It's also available as often as you have death runes, meaning it's more likely to be up in case of emergency.
Conversion will constantly drain your runic power in exchange for health. The issue here is that if you aren't using your runic strikes, you aren't powering your rune regeneration talents, which means your damage output - and runic power generation - will drop like a rock. Still, if you find yourself with a lot of runic power and not much in the way of healing, this may be a decent option for you.
Death Strike, Blood Presence, and other old standbys
Death Strike is definitely a dependable standby for any death knight, even if it doesn't do as much healing for DPS death knights. It's especially handy for frost death knights, who can slip it in to their rotation where they'd normally use Obliterate without missing a beat. It really shines when paired with Glyph of Dark Succor. If you're doing your dailies, soloing, or even just beating up a lot of trash, the glyph can make those Death Strike heals incredibly beefy.
Blood Presence is the traditional tanking presence, and does increase your threat generation, it's true. However, it also gives you a bigger health pool and more damage resistance, which means if you pull damage or get into stuck in the fire, it will help you survive. If you have to use it, you'll want to stop all attacks at once so you don't pull aggro, or so the tank can peel the mob back onto themselves, of course. The threat does make this sort of a last ditch defense in PvE, but in the end, it will give you some extra survivability. Just remember to switch back to your DPS presence once the coast is clear.
Army of the Dead, despite being one of our more hated abilities, is a survival tool in the right situations. While channeling it, you gain a damage reduction equal to your dodge and parry chances, and once they're summoned, the ghouls will taunt mobs, meaning said mobs are less likely to be attacking you. Now, the issue here is that, because of that taunt, you should never use Army of the Dead in a place where random taunts could cause issues, such as against a mob with a cleave or cone attack that a taunt could turn on the healers or DPS. That means Army of the Dead becomes a bit of a panic button when a wipe seems imminent.
That said, you can turn this around by using the Glyph of Army of the Dead, which takes away the taunt factor. If you have this Glyph, Army of the Dead becomes a short term damage reduction cool down while channeled, followed by a small burst of DPS from the ghouls, who shouldn't cause much trouble unless you have issues with proximity pulls.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.