What this is not
This isn't a strategy guide or such. To know what is happening in the fight, go read a bossguide at the appropriate sites.
This post is meant as an explanation of how Immortalis tries LK10, and how I handle the strategy as a rogue.
In phase one, not a lot is going on that is of concern for a rogue. The only thing we really have to watch out for is the Necrotic Plague.
If you get this debuff, you need to run towards the tank taking care of Shambling Horrors and Drudge Ghouls and wait until your designated cleanser makes the debuff jump to the ghouls (or force it to jump by cloaking it).
Other than that, you just DPS the Lich King as hard as possible, and help out the tank with Tricks.
When the phase ends, the safest spot to run to would be the ranged and healers clump, because your Horror tank might still have the Necrotic Plague and we don't want that to spread.
A short phase follows where you fight some ghost copies of your teammates at the sides of the platform while the ranged shoot at frost orbs. Not a very interesting phase, IMO. Tricks them to your tank and nuke them asap.
In phase three, there's two things that require our attention. First, the defile. Always be aware of your position on the platform - if you should get a defile, you DON'T want it to happen under your raid, you have a few seconds to sprint to the edge and drop the defile out of harm's way.
The other issue are the valkyr, which pick up a random raid member in an attempt to throw him/her off the ledge (not a very cool death but it gets the job done).
The problem, then, is combining the two. Stopping a valkyr from throwing off a raid member is easier said than done when a defile is in your way.
We always try to "control" the path valkyr will take by dividing the circle in the center into two slices of pie, and depending on defiles we position ourselves somewhere when a valkyr is coming.
Collapse onto that point, then spread out again to minimize defile risk. In the screenshot, you can see how we're all on the right side (apart from a naughty shaman who recently got a defile).
The orange arrows are possible paths valkyr will take, and the red arrow shows the danger the shaman is in - if a valkyr were to pick him up, he would be thrown off on the other side, away from all of us - we would not be able to stop the valkyr in time.
Similar short phase to Phase 2, nuke the spirits. They come a bit faster this time and you don't want several of them up when the next phase begins.
In this phase, the sentence "death from above" comes to mind. There's a bunch of spirits coming from above, and the ranged has to kill them. Nuke the Lich King, but beware of death from above. They HURT.
Also, in a suprising twist, the Lich King randomly tries to suck the soul out of people using Frostmourne. If you survive the initial attempt, you end up in Frostmourne, where Arthas' fathers soul is battling yet another spirit. As a rogue, you nuke the spirit and interrupt its cast.
In this shot, the spirit was already dead - I didn't want to risk the fight for a screenshot since we were having a great attempt.