Tip: The second you hit 84, stop whatever you're doing and head back to Org/SW (you are horde, right?). Grab the twilight highlands and get moving on it.
The only exception is that, if you don't have Therazane dailies open yet, go do all the Deepholm quests until they're available. You need those guys open asap so you can get their tabard.
Thanks for the heads up. I didn't have the Therazane dailies yet, but I was like 5 quests away from them. Unlocked them and did them all in about 20 minutes.
Now I'm working on the questline to get to Twilight, but I have to go out. I'm about 10% through 84 now!!! Almost there!!!
EDIT: What is the urgency towards going to Twilight? I don't know much about that area or what happens or what options open up to me at the end game.