Most of the components for leatherworking are received from skinning. You can avoid getting skinning as a profession if you just buy the components off the Auction House.
Since patch 2.4 was implemented you can now train up to Artisan Leatherworking at any trainer available. To get your skill past 300 you will need to see the Master Leatherworking Trainer that is located in each factions appropriate starting city for the Burning Crusade in Hellfire Peninsula, Honor Hold and Thrallmar.
The first part of this guide is simple. Make some Light Armor Kits and Cured Light Hides. You can give the Light Armor Kits to an alt if you have one. You won't need to keep the cured light hide. These two steps will get you to 55.
Make sure you keep your Cured Medium Hides because they will eb used to go from 125-150 and you will most likely have to make some more to complete that step. Any of the green items you craft you can try to sell on the Auction House or save for disenchanting supplies.
The Cured Heavy Hide you make will be used later in this section so make sure you keep them. Some of these items may start selling on the Auction House to twinks and people leveling up. You will also get Heavy Armor Kits which you can use yourself or give to alts. The last step requires an Iron Buckle, it is made by a blacksmith or you can get one off the Auction House.
This part can be very profitable as a Leatherworking. All of the Nightscape items you make can be sold on the Auction House for money or sold directly to disenchanters. These make good twink or alt items as well.
Wicked Leather recipes you will be making used to be hard to get but are now apparently trainable at any Leatherworking Trainer, these should sell decent on the auction house as well.
There are a lot of items you will be crafting in this section that sell well. I must warn you that the last parts will be more difficult than some of the other professions to finish, but this is the fastest way we've found toc omplete them. From 340-355 you will be required to make Felscale Breastplates which require Fel Scales. These come off Basilisks and few other creatures in the Outlands and may cost a lot of money to buy in the Auction House.
Heavy Clefthoof Boots are bought from Fedryen Swiftspear at the Cenarion Camp in Zangarmarsh, you must have friendly reputation with the Cenarion Expedition. This step will be pretty costly because of the Thick Clefthoof Leather.
Drums of Battle come from the Sha'tari Quartermaster in Shattrah City, Almaador. You must be honored with The Sha'Tar.
Drums of Panic come from the Keepers of Time Quartermaster, Alurmi. They require Honored with Keepers of Time.