Before going to the dungeon I did the following to optimize my chances of survival:
1. I got the first dragon shout in the main quest, relentless force.
2. I earned Lydia.
3. I found a nice 2-handed sword, an Ancient Nord Greatsword.
What I was interested in in Lost Valkygg was two Draugh Deathlords, but to get to them I had to defeat a couple of Restless Draugh and a couple of Draugh Wight. With the help of a few potions and Lydia I wasn't slaughtered and I could advance victoriously!
The first Deathlord I encountered was patrolling a large hall. Be warned - he hits very hard! Even though I was covered in heavy armor, I was one-shotted every time I didn't move or strafe fast enough!
Since I had specialiced in 2-handed weapons I decided to approach him when he would have no line of sight to me. This happened when his patrol brought him into a seperate room behind the chest he seemed to be guarding. This made it possible for me to jump him at a minimal distance of approximately 3-4 meters. His first action was to perform a disarm shout. Only through the miracle of trial and error did I learn to get to cover at this point of the battle. I then drew him out into the open and had Lydia rain arrows down on him. She would often be one-shotted and be out of battle, but would then come back to fight. Every time Lydia was down, I would hide in cover behind solid structures and exactly the moment when she rejoined the battle I would engage the deathlord. I kinda used hit and run attacks for 3 minutes, using my relentless shout and my power attacks to keep him staggered, before running into hiding again. When he came down to 10% health, he seemed to become rather passive and just stood looking furiously at me, without actually doing anything aggressive. At the end, he had to bite the dust and left me a nice Ebony Bow on his corpse and a unique dagger in a nearby chest.
Then I began looking for second Deathlord, whom I had read about. I was quite confused when I had searched all the way through the dungeon without finding him, and now stood in front of an exit to Skyrim. I was even more confused when I was instantly attacked by this very deathlord the second I popped up outside the dungeon. Fortunately, this deathlord did not one-shot kill me, so I quickly fled 20 meters and was delighted to see how the deathlord had not only upset me, but also a couple of nearby ice trolls who didn't hesitate to join the fight. The ice trolls finished the deathlord rather quickly and I then finished the ice trolls just as quickly using my new Ebony Bow. On the deathlords corpse I found the Ebony Greatsword.
TL;DR:
1. Go to Lost Valkygg near Labyrithian.
2. Defeat first deathlord:
- Don't get hit at all!
- Use power attacks and relentless shout to keep deathlord staggered!
- Have a follower attack him constantly!
3. Loot Ebony Bow.
4. Go through dungeon and use exit the in the end.
5. Defeat second deathlord.
6. Loot Ebony Greatsword.
I did this at level 1 on master difficulty. If you have difficulty doing this, try lowering the difficulty settings in the options -> gameplay menu.
Have fun!