Use Single Target dps on Lichking, AOE should not be used.
Phase 1
Position:
Lichking
Main tank and melee
Ranged and healers
Off tank with Ghouls and Shamblings

Infest:
Every person in the raid will take around 7k dmg and will take increasing shadow dmg every second afterwards
This effect is removed when the target has more than 90% health
Necrotic Plague:
Every 15 seconds Lich King applies the Necrotic Plague debuff to a player
The Plague is a dot which deals 50k dmg to its target every 5 sec
Whenever the debuff is dispelled or its target dies, it jumps to a nearby unit - including adds
How to deal with it?
The debuffed player has to run next the off tank with the adds and dispel him there, so the plague will jump to an add
Phase 1.5 and 2.5 - Transition phases - Everyone except off tank - Off tank
At 70% hp transition phase takes place and lasts for 1 minute
He will begin casting Remorseless Winter, so the raid must flee on the edge of the platform to get out of the spell
Transition phases are almost just about controlling the spawning adds
The off tank will move the remaining Shambling(s) and the Ghouls to his spot faced away
The main tank will drag the missed ghouls into the stacking raid so they can be killed
Raging Spirits will spawn during this fight every 20 seconds
It's a target's spirit and the target will be attacked, but the off tank will taunt it asap and face it away from the raid
When the 3. Spirit is summoned, Lich King casts quake, which destroys the outer ring of the platform
The raid has 2,5 seconds to move away from the edge, onto the platform
If a player has Nectrotic Plague debuff in the start of the transition phase, just run away 10y from the raid to get dispelled, the Plague will no longer jump
There will also spawn Frost Orbs which heads toward the raid but are easily killed by a ranged dps
When the phase is over, kill the remaining spirit, while the main tank is tanking LK
Phase 2
There are two major abilities to be aware of in Phase 2. Valkyries and Defile
Valkyr:
The Valkyr pick up a raid members, carry them to the edge and drop them to their death
To avoid this, everyone should stack near the center of the platform, so the Valkyr has to travel a long path
The Valkyr can be stunned and snarred and should be nuked fast
Defile:
Defile is an AOE which is placed on a random raid member (a big black circle on the ground)
When it deals damage it grows larger and increasing its damage, and is the major reason to wipes
To avoid this, the raid must be spread out close to the outer edge of the platform
DO NOT stay in the middle. If you leave a Defile in the middle, the incoming Valkyr won't have as long a path
Phase 2.5
When Lich King is at 40% hp he casts Remorseless winter again and starts the transition phase.
This time 4 Spirits will spawn every 15 seconds
After 1 minute phase 3 starts

Phase 3
During phase 3 LK continues to cast Defile
Instead of Valkyr, he summons Vile Spirits
At the start of phase 3 the remaining Raging Spirit should be killed by melee while range deals with Vile Spirits
Each Vile Spirit have 66k hp. They will move towards a raid member and explode when they reach their target
Ranged should kill them before they start moving
Phase 4
At 10% hp Lich King casts Fury of Frostmourne which kills every raid member
After some time everyone is resurrected by Terenas, and players can finish off Lich King without worrying about anything