Archavon Trash

The trash before Archavon is pretty simple, tank and spank, and when the use Cave in, move your caster base out of the falling rocks.

Archavon

Archavon himself is pretty simple once you understand how to control him. If you keep everyone within melee range, he won't jump and leave clouds. Knowing that, just keep everyone in melee range, and he becomes a tank and spank. Heal through the rock shards he shoots (Devotion Aura and Stoneskin Totem help here), and keep your taunt button close for the off tank for when the main tank gets grabbed. Once the MT gets free, run back, taunt him back, and continue.

Noth Trash

There are two types of pulls for Noth trash: 2 Ghouls and 2 Slimes, and lone and double gargoyles. For the ghoul/slime packs, keep your party fairly far back, and pull the ghouls a good distance. DPS them down and ideally they should both be near dead by the time the slimes approach. Try to avoid tanking both slimes and ghouls at the same time, as slimes hit for 6k on plate, but move at about 50% movement speed.

For Gargoyles, it is a DPS race, as they stack an undispellable DoT on the whole group that stacks and will eventually become unhealable. Also, when the gargoyles hit 100k health left, they start casting stoneskin. If the gargoyle doesn't die before it finishes casting, it goes immune and restores a large portion of its life.

Noth the Plaguebringer

Move your group to the back left corner of the room, just under the balcony. Noth himself is more or less a tank and spank with constantly spawning adds. Chances are you'll have to taunt the adds when they get close, so keep a mouseover taunt handy, and if you have a paladin, the AOE undead stun is good for grabbing the spawns as they run by. After about 4 waves of spawn, Noth will teleport to the balcony and becomes untatargetable. Beefier skeletons will continue to spawn for this phase, but if you can keep up with grabbing them you should be ok. After about 3-4 of these waves, Noth returns to the battlefield. He behaves just like the first phase. If you can kill him before he teleports away, great, if not, the second teleport phase gets messier, as skeletal mages will spawn and start AOEing. If you run toward and taunt them, this phase is difficult, but not impossible. If you can make it through the skeleton mages, Noth will again return, and its just a matter of burning down the last of his health.