Easy. If you just want to do it, it's a WQ, you can search for a group when you get there (west side of Eastern Plaguelands).

But, you will want to do the Ice Crown rares too, likely, so don't neglect the questline, it goes away on launch.

For that, you should have gotten an auto-accept quest called An Urgent Request. That will get you to talk to Genn Greymane in Stormwind, at Lion's Rest.

That questline will send you to a brother from the Light's Crusade at the southern gate of the Trade District in Stormwind, then off to collect reports and kill a dozen mobs, and then back to Stormwind to turn in the quest Return Of The Scourge. When you do, there will be a second quest to pick up from another NPC by your turn-in, which is the quest that sends you off to fight Nathanos. But, the chain itself continues with your introduction quest to start Ice Crown.

It's a good run.