Shadow-frost has been nerfed into the ground and now you may wonder about finding another viable BG spec and arena spec. Frost is coming out on top because of the insane burst it can output, and it's survivability with unbreakable armor. 

   With Battle Ground spec (frost), you can use glyph of Frost Strike and Hungering Cold. In this spec, you will have very high survivability. Hungering Cold is used to control, which means that you could freeze an opponent while killing another. It also puts frost fever on targets, allowing you to run into a group of enemies and doing HC- Death-chill Howling blast for massive AE damage.

Your biggest burst will come from frost strikes which hit through plate, as will Howling Blasts. To take down a healer you will need to be precise with silence, spell breaking and be in unholy presence. Get 130 RP, you should make sure to have frost fever on the enemy and then silence them, pump out 4 frost strikes followed by a howling blast. Those 6 things will take 6 seconds, so after strangulate is up and the healer isn't dead you're going to have to mind freeze to break spell casting, and since mind freeze cost no RP.

Fighting vs. DPS classes that can kite you (Hunter, Mage, Warlock, etc) are actually quite easy to get to with this spec. Warlock will try to fear you, but you just need to put on lichborne and then anti-magic shell after that, followed by mind freezes and strangulate. Having Mind Freeze cost nothing is amazing because you can just keep spamming it every 10 seconds. When spirit wolves, treants, mirror images are summoned pop unbreakable armor and you are set. Death-chill Howling blast on enemies that are below around 4k health will guarantee a kill. Don't forget to anti-magic shell whenever you can as it will allow you to spam frost strikes more often. 

   Classes like Paladins can heal themselves while doing crazy burst, they are tougher to kill. You are going to always have to pressure them into needing to heal, meaning you need to break heals whenever possible, and don't use death-chill until they have bubbled. Popping unbreakable armor at the beginning of the fight is the safest thing to do when fighting retribution.

   In this build, the major difference is no self heals. You'll only have ghoul sacrifices to rely on for heals if your healer can't heal you, but the biggest difference is increased damage and virulence. Because frost specs require you to have frost fever on the target at all times. Virulence can help with that. Another thing you can do is use hungering cold on an enemy to force a trinket or take him out of the fight for 10 seconds. HC is 1 minute CD while trinket is 2 minutes. If the other teams comes rushing in on us, try and get both of them in one hungering cold right away, and start by attacking one of them, taking the other out for 10 seconds or forcing a trinket. Forcing an early trinket or defensive CD can turn the match to your favor immediately. 

   HC is stupidly overpowered but much underestimated, just use it. It's like a wyvern sting but it shares diminishing returns with some moves.Hungering cold shares diminishing returns with polymorph, gouge and sap related moves so remember that if you try and use hungering cold on a target after one of those are used on the same target, the duration of HC will be only 5 seconds. Diminishing returns are on 35 seconds, so if your partner doesn't have any of those moves, do not worry.

If you suspect a Rogue, keep pressing you blood boil ability, this will knock a Rogue out of stealth and it is very cheap and effective to do.
For frost, you'll want attack power, strength (frost strike) and some crit. But the game-breaking stat that frost must have is spell penetration. There is nothing worse than having your main burst resisted and then you need to rebuild RP. Strangulate can be resisted and lots of your frost moves. To counter this take about 100-120 spell penetration to make sure nothing is resisted. 35 on cape and then gem your blue sockets +20 spell penetration.
If you like PvE, getting the frost strike sigil a must because it can up your crit damage on frost strike by amounts up to a thousand. You will need some resilience but PvE geared Death Knights usually totally obliterate everything in their path but not without cost as they will be killed very quickly.