Buff maintenance is really important for DK, keep them heals rolling and don't let your armour fall off. It adds a ton of healing.. Pre-apply vigor before engaging a fair fight and re-apply often.

A ton of BG builds focus on root/snare/CC lockdown in noCP. A snare cleanse/immunity is crucial to your survival. You're a way more attractive target if you're locked in place. Basically two ways you can approach this, forward momentum, or race against time. I prefer Forward Momentum with DW's Quick Cloak for speed. The Major Evasion is really handy against a lot of builds.. Blastbones, Shalks, Spin to Win, Dawnbreakers, Northern Storm, all AOE.

With eternal vigor in heavy, you can semi-spam cauterize if you find yourself in trouble. I run 2h/DW but I hate dizzy.. I run fossilize where most will run dizzy on the 2h bar. This usually gives you a 2 GCD advantage on a single target. Most are going to break free -> roll out of the fossilize root. I typically follow up a fossilize with noxious, if you see them go for the roll dodge, Leap into execute. Leap can't be dodged and execute should follow up as their roll ends.

GDB sucks imo.. The only reason I would consider running that is if you could afford Mag+Heroism pots. That way you keep all 3 major recoveries and spit out ultimates for more sustain. EDIT: Unless you're running a crazy health pool.

Blood craze offers another small HoT you can stack with Vigor.. The damage is only worthwhile with Master weapons, though.

I'll also add:

The key to winning a fight is not dying; you can't do anything if you're dead. I know that seems self-evident, but it's not as simple as it would appear to be on the surface. There are several factors to consider.

First is damage mitigation. This is damage that you don't take. It's free. If you don't get hit, you don't lose health that you'll have to make up by healing. Having to heal means using skills (and thus time) and resources. This is best accomplished by using a rock, a tree, a wall, or some other object. The more you keep a solid object between you and the guy who's beating on you, the better your survival will be. Mitigation also includes your resists and crit resists. The higher those are, the less damage you take in general.

Second is active defense. This includes blocking, dodging, shields, purges, and the like. These things have a cost associated with them, but that cost is lower in both resources and time than what you would spend recovering from the damage you otherwise would receive. Take, for instance, your friendly neighborhood Warden's burst combo. If he lands his Sub Assult / Dizzy / Dawnbreaker combo, you're looking at potentially 15k - 20k damage. To recover from taking that damage will cost you resources for heals and a few seconds to get that health back, assuming you're able to. A well timed block and/or dodge roll can save you from taking most if not all of that damage. This is where experience comes into play. You must learn to recognize when those big damage hits are coming and defend accordingly.

Third is healing. Oh carp! I'm hit! Now is the time to heal. If you can't avoid damage and can't defend against it, you eat it. Healing costs a LOT of resources and time compared to the above defenses, so you want to have to do it as little as possible. DK has a great toolkit for healing, specifically Fragmented Shield, which gives you major mending. As a StamDK, you have a very limited magicka pool, so you only want to use Fragmented Shield when you really need to. In general, if I'm taking damage, I keep Vigor up more or less all the time. If I take more damage than Vigor can keep up with, I burst heal with Rally. If those aren't enough, Fragmented Shield, Vigor, and Rally as needed to stay alive. This may require disengaging to hide behind a solid object (see above) to buy enough time to recover. Also, use tri-stat potions to keep resources up, especially magicka for Fragmented Shield. They also do a good bit of healing.

These three things, each on their own, will not save you. You have to do all three, all at the right times, and often all at the same time. Again, this is where experience counts for everything.

There's a fourth factor, and that's pressure. If you can keep up a high amount of damage on your opponent, he has to heal and defend, which means less opportunity for him to do bad things to you.

Defense and aggression have to exist in balance; you have to push your opponent when the time is right, and defend when the time is right. Being all spank and no tank will get you dead if they burst you down and you're not healing or otherwise defending. Similarly, going full turtle mode will allow them to gradually whittle you down to where a burst / execute combo will finish you off. You have to do both things. Defend and attack as the fight dictates while looking for your opportunity to burst your opponent down.

Finally, above all things, pick your fights. A wise man once said, "You got to know when to hold 'em. Know when to fold 'em. Know when to walk away, know when to run."

TL;DR: Git gud