I'm leveling only VIA questing, and so far did this route: Starting zone-->The Barrens-->Stonetalon mountains-->Hillsbrad Foothils-->Ashenvale-->Thousand Needles (in TN, i only did the quest in the freewind post and to the west in the small camp only).

So, now i reached level 30, and i don't know where to go!
I got a lot of advice, including Desolace, Arathi Highlands, The Shimering Flats in TN & STV.
which one is best for me to level right now? and what should be the route from now on?
Sorry for the newby question, it's just with my previous alliance 70 mage, i used a leveling guide and now I'm doing it on my own.

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I know i'm a Newbie, i start just 2 weeks ago (19/09/06)..be easy :P

Also have a look at our recent post about "Leveling Improvements for Patch 2.3":

An excerpt:
We've also added approximately 60 new quests in Dustwallow Marsh. This should help players who find themselves lacking quests in the 30-40 range. The Steamwheedle Cartel is building the new town of Mudsprocket in south-west Dustwallow Marsh, so you'll have to wait until construction is complete to learn more about these changes.

2.3 Isn't quite out yet, but hopefully it will be there soon, before you reach 40 perhaps :)