The great part about getting on board with a new spec at the end of an expansion is that it's easier than ever to get gear. If you're wandering around Timeless Isle regularly, there's a chance you've stockpiled a few extra pieces of Timeless plate gear. if so, switch to your blood spec, right click on them, and you've got a great tank starter set.
alternately, you can head over to Niuzao Temple and check out the vendors there. Item level 489 gear from the first patch of the expansion can be purchased for Justice Points. More importantly, if you've run enough Throne of Thunder to be friendly with Shado-Pan Assault, you can buy item level 522 tank gear for most of your slots at friendly reputation from Ao Pye. If you don't have friendly reputation yet, it should be relatively easy to get by running Raid Finder (assuming your DPS set is good enough to queue, of course). You can get up to 2999/3000 in neutral off of trash mobs, then you'll only need to kill one boss to get over the top. Of course, you might as well just run a few wings in a row. They're already open and you'll get even more chances for tank gear. Be sure your loot specialization's set to blood.
The one slot that's not so easy to get an upgrade for is your weapon. With enough Timeless Coins, you can get a Yak-Herder's Longstaff on Timeless Isle, but in a pinch, you can use the weapon from your DPS set. Just be sure to go switch the runeforge to Rune of the Swordshattering before you head into that dungeon or raid.
Of course, the next question is figuring out the stats on the gear you get. The rule of thumb for most death knights is that you get as much stamina as you need to survive the fight, then stack on the mastery. You'll generally need to discuss with your raid leaders or healers how much stamina is enough for your content. If all you're doing is flex raids or lower, any stamina you get off base tanking gear will probably be more than enough and you should focus on getting mastery. If you need threat, you'll want to cap your hit and expertise at 7.50% each, then grab avoidance for Riposte. Unlike in Cataclysm, avoidance isn't as easy to balance as keeping both stats balanced. The incredibly simplified explanation is that parry is way more valuable than dodge in most situations. Of course, there's still minimum amounts of dodge you want if you're min/maxing, but if you're just dipping your feet into the spec or doing some flex raid tanking, focusing on parry for your avoidance needs is probably good enough.
With this in mind, your gems and enchantments should focus on mastery where possible. That means Fractured gems for yellow slots, Puissant gems for blue slots, and Fine gems for red slots. For reforging, you can reforge to mastery, or take the opportunity to balance your avoidance stats or adjust to hit or expertise caps.
Talents and glyphs
Roiling Blood is probably the best tank talent on the first level. Since you'll be getting free Blood Boils anyway, and since Blood Boil refreshes diseases on your main target, Roiling Blood means your diseases stay up on trash packs indefinitely. Purgatory is easily the preferred choice for tier 2. A Get Out of Death Free card for a beginning tank is a lifesaver. On Tier 3, I'd prefer Death's Advance. Never underestimate having superior speed when positioning a mob. On tier 4, I personally prefer a Death Pact, especially when backed up with Vampiric Blood or used to avoid dying after Purgatory just saved me. On tier 5, Runic Corruption actually gives the most DPS, thus allowing for more threat, whereas Blood Tap means you can unleash an extra Death Strike right when you need it most. On Tier 6, I prefer Gorefiend's Grasp for easy add wrangling, though Remorseless Winter can be nice for keeping wrangled adds wrangled.
On the side of Glyphs, Glyph of Death and Decay is probably one of my favorite "training" Glyphs for tanks. With this glyph down, even if you lose aggro on a mob, you'll have more chance to drag it back to you since it'll be moving slower. Glyph of Vampiric Blood is good if you trust your healers or don't think you'll need the initial big heal. I tend to take it, since I figure I can use Death Pact or hit Empower Rune Weapon and throw out a few quick Death Strikes if it comes down to that.
Death knights do have less passive armor and damage resistance than other plate tanks, but they make up for it by having a wide array of cooldowns and major self-healing ability.
The basic rotation of the death knight tank is maximizing death strike usage. Since Death Strike heals us for a specific percentage of damage taken in the last 5 seconds and creates a shield for the same amount, being able to use it right after you took a lot of damage is important, so, however, is using it constantly to have that shield. In addition, it's usually considered good practice to have a pair of frost/unholy runes on cooldown at all time. Remember, if all else fails, you can use one of our many cooldowns until you're able to Death Strike again. If you know you won't be able to use Death Strike for a while, use a cooldown like Icebound Fortitude or Vampiric Blood instead.
As we've said in other columns, of course, the art of being a tank is just that, an art. Sometimes what you really need is experience. You'll need to know fights, not just to explain them to other players in Raid Finder, but to know when burst damage is coming so you can use your cooldowns or queue up runes for a quick Death Strike. You need to know when the boss uses a massive armor debuff so you can work with your tank to taunt off each other. In the end, though, that's one of the reasons I recommend giving tanking a try, here at the close of the expansion. The type of quick thinking and planning you have to do will serve you will even when (or if) you switch back to DPS for the next expansion.
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.