I think this guide to Gnomeregan done by @Cassandri of HoTs & DoTs deserves a post all to itself. For those of you who have been playing Horde all your life and now find your low level toons thrust into Gnomer from random queues, here is your golden ticket to success.
You can find similar posts from Cassandri for Razorfen Kraul, which the Alliance players will probably be less familiar with since it’s located in the Barrens. Also Blackfathom Deeps, which is pretty equally known by players of both factions, I think. And you can find a short version for Scholomance if you need one as well.
You might be able to find a full list (for walkthroughs that get added after this post of mine) by checking out This Link.