Prerequisites:
-revered with Ogri-la
-be a warlock or hunter, alternatively have a party with you or be uber skilled :P
-have lots of spare Apexis Shard
-have disenchanting to at least skill 275
If your server is anything like mine, then large prismatic shards (LPS) are extremely expensive, they go easily for 20g or more on my realm, average price seems to be 25g each one.
Basically the idea is, where you do the The Relic's Emanation quest (play the simon says game on the artifacts) there are 4 small artifacts and one large one.
This should be done at the artifact north of the skyguard base.
First of all I suggest actually doing the quest, this gives you a run speed buff which is essential to doing this. I also suggest clearing all the mobs in the artifact.
Once you have the buff and the area is clear then you should proceed to the larger game and insert your 35 shards.
I normally play this large one for the first 1-2 goes then I just let the timer expire and the big Apexis Guardian gets summoned anyway.
The moment he gets summoned you want to start kiting him, keep dots ticking on him and run him through the skyguard base, then through ogri la, I then take him back around the big crystal to my left and back into ogri la, then back through skyguard base etc :P
This video should explain how to do the kiting quite well (I can't take credit for the vid)
[ame="http://www.youtube.com/watch?v=fGc3JcpGUqA"]YouTube - Athenia vs Apexis Guardian[/ame]
Once you have killed him then you should be able to loot one Apexis Crystal and usually a green as well for good measure.
Take this crystal to Jho'nass and trade it in along with 50 shards for the blue wand Cerulean Crystal Rod
DE this into a LPS and = profit!