So, you want realm or world first level 90, but your not sure how to do it?
Well if you have 25+ other people to support and help you, here is probably the easiest, safest and quickest way to do it. Why is it quickest? Well simply put, the more people you have helping... the quicker it will go.
For this guide we will use 20 spawners (in a raid or solo) and 5 killers (in a party)... however simply adding more spawners until you cannot aoe the mobs down as fast as they spawn means the proccess can be infinately faster.
Firstly head your team into the Jade forst you want to head to here:
Where you will be able to pick up a quest line from a dead mob on the floor.
The Sprites' Plight - Quest - World of Warcraft.
Basically, as you follow this quest line you will get to a Spirit of a panda who will eventually offer you this quest: Back to Nature Back to Nature - Quest - World of Warcraft
You are given a quest item, spirit bottles. Which when thrown on the ground in a certain area as a chance to spawn a hostile mob (around a 60-70% chance of spawning a hostile one)
Head up to the spawning area here:
And have your spawner guys start throwing bottles on the floor, whilst your killing team starts aoe'ing.
Using this method, you are able to maintain at least 12-15 million exp an hour with 20 people. With 30 people spawning this can go upto 20 million exp an hour.
As far as I am aware, there is no other method as effective as this currently known.
Enjoy