NOTE: The first quest has a level requirement of 55, but higher is desirable to complete necessary quest content. This is a long chain, involving alot of work and world travel, but the reward is invaluable - the key to the mighty Onyxia's lair. You will reap the benefits of raiding Onyxia only upon completion of this series.

Walkthrough - Drakefire Amulet:

1) Go to Kargath and speak to Warlord Goretooth in the tower. Click his conversation icon repeatedly to receive Warlord Goretooth's Command. Use this item to receive the quest, Warlord's Command.

Warlord's Command
Slay Highlord Omokk, War Master Voone, and Overlord Wyrmthalak. Recover Important Blackrock Documents. Return to Warlord Goretooth in Kargath when the mission has been accomplished.
Important Blackrock Documents: 0/1
War Master Voone slain: 0/1
Highlord Omokk slain: 0/1
Overlord Wyrmthalak slain: 0/1

2) You will need a full party of five for Blackrock Spire(BRS). The documents spawn randomly at one of the three bosses above and only one per instance can be acquired. This quest may NOT be raided!

3) Upon completion of Warlord's Command, you will receive the quest, Eitrigg's Wisdom.

Eitrigg's Wisdom
Seek counsel with Thrall's advisor, Eitrigg. He can be found in Thrall's chamber.

4) Speak to Eitrigg in Thrall's Chamber, then return to Thrall. He will give you the quest, For the Horde!

For the Horde!
Travel to Blackrock Spire and slay Warchief Rend Blackhand. Take his head and return to Orgrimmar.
Head of Rend Blackhand: 0/1

5) You will have to attend a raid of Upper Blackrock Spire (uBRS) to get the head of Rend Blackhand. Do so, and once again return to Thrall in Orgrimmar. All the occupants of Orgrimmar will receive a buff upon turn in.

6) Thrall will tell you to seek out Rexxar, who roams from north Feralas, through Desolace, and into southern Stonetalon Mountains.

7) Rexxar will give you the quest, The Testament of Rexxar. You are to deliver Rexxar's Testament to Myranda the Hag in Western Plaguelands.

Testament of Rexxar
Deliver Rexxar's Testament to Myranda the Hag in the Western Plaguelands.

8) Find Myranda the Hag near Uther's tomb, south of andorhal, standing on a tree stump.

9) Myranda the Hag will give the quest, Oculus Illusions.

Oculus Illusions
Travel to Blackrock Spire and collect 20 Black Dragonspawn Eyes. Return to Myranda the Hag when the task is complete.
Black Dragonspawn Eye: 0/20

10) Once again, you will have to raid uBRS and collect the Black Dragonspawn Eyes. They drop 1-2 at a time and are common.

11) Return to Myranda the Hag with 20 Black Dragonspawn Eyes. She will give you an Amulet of Draconic Subversion and the quest, Emberstrife.

Emberstrife
Travel to the Wyrmbog in Dustwallow Marsh and seek out Emberstrife's Den. Once inside, wear the Amulet of Draconic Subversion and speak with Emberstrife.

12) Travel to Emberstrife's Den in Dustwallow Marsh. It is the cave along the cliffs to the very south. The Amulet of Draconic Subversion will transform you into a Black Scalebane once inside Emberstrife's Den. While disguised, speak to Emberstrife. He will behave as an NPC.

13) Emberstrife will begin a mini-series of quests titled The Test of Skulls. The first such quest in this series is The Test of Skulls, Scryer.

The Test of Skulls, Scryer
You must find the blue dragonflight drake champion, Scryer, and slay him. Pry his skull from his corpse and return it to Emberstrife.
You know that Scryer can be found in Winterspring.
The Skull of Scryer: 0/1

14) Travel to Winterspring with a good group of five* and enter the caves of Mazthoril, south of Everlook. Work your way in, and slay Scryer.

NOTE: The drake kill quests may NOT be raided!

15) Return to Emberstrife using the Amulet once again, and get the followup, The Test of Skulls, Somnus.

The Test of Skulls, Somnus
Destroy the drake champion of the Green Flight, Somnus . Take his skull and return it to Emberstrife.
The Skull of Somnus: 0/1

16) Somnus can be found in Swamp of Sorrows, wandering in an arch up and down the zone between the Pool of Tears and the beach.

17) Return to Emberstrife as above, for the followup, The Test of Skulls, Chronalis.

The Test of Skulls, Chronalis
Guarding the Caverns of Time in the Tanaris Desert is Chronalis, child of Nozdormu. Destroy him and return his skull to Emberstrife.
The Skull of Chronalis: 0/1

18) Travel to Tanaris. Along the east edge of the zone is a mountain. Enter the area to find two low level drakes, and finally, Chronalis, guarding the door in the back.

19) Return to Emberstrife for the followup, The Test of Skulls, Axtroz

The Test of Skulls, Axtroz
Travel to Grim Batol and track down Axtroz, drake champion of the Red Flight. Destroy him and take his skull. Return the skull to Emberstrife.
The Skull of Axtroz: 0/1

20) Go to the Wetlands and enter the Dragonmaw Gates region, the curved valley area in the east side of the zone. Travel down the valley a ways and you will find Axtroz.

21) Return to Emberstrife to receive the followup, Ascension...

Ascension...
It would appear as if the charade is over. You know that the Amulet of Draconic Subversion that Myranda the Hag created for you will not function inside Blackrock Spire. Perhaps you should find Rexxar and explain your predicament. Show him the Dull Drakefire Amulet. Hopefully he will know what to do next.

22) This quest is to simply find Rexxar again. Rexxar will give you the final quest, Blood of the Black Dragon Champion.

Blood of the Black Dragon Champion
Travel to Blackrock Spire and slay General Drakkisath. Gather his blood and return it to Rexxar.
Blood of the Black Dragon Champion: 0/1

NOTE: Only one person can get the blood off General Drakkisath per raid! For this reason, please organize a list of people who need it, or simply roll each time until everyone is complete.

23) Return the Blood of the Black Dragon Champion to Rexxar, and receive the Drakefire Amulet, a necklace.

24)Keep the Drakefire Amulet in your inventory to be allowed access into Onyxia's Lair when you raid! You need not WEAR the amulet, simply have it on your character.

For more indepth coverage of instances, check this guide out!