So I'll try here.
Complete Leatherworking Guide:
To start leatherworking ask a guard in the nearest city. At the apprentice trainer you can get new patterns. Those patterns tell you the items you need to craft the selected item. If the Item is Orange you will get a skill point up. If its yellow you have a 66.6% chance (I think) of getting a skill point. If its green you have a 33.3% of getting a skill point. Getting a skill point increases your overall leatherworking ability. The points below indicate your skill level:
Apprentice: 1 to 75
Journeyman: 75 to 150
Artesian: 150 to 225
Master: 225 to 300
Apprentice: Local starting spot
Journeyman: Near Apprentice trainer (might be the same guy)
Expert: Ironforge, Darnassus (150+)
Artisan: Darnassus (225+)
At this point you must choose between Tribal, Elemental, and Dragonscale.
Tribal: You start the tribal leatherworking as a series of quests starting in Feathermoon (Ferales). The guy you need to speak to is near the gryph path. You will need lots of turtle scales and wildvine. Its almost easier to buy the items in the AH at times then to farm the turtle scales.
Elemental: Starts in Searing Gorge (SE portion if memory serves)
Dragonscale Leather: Azshara Along the southern edge of the Ruins of Eldarath, up on the cliffs.
Post by Genious:
Making money with leatherworking is currently not the best idea. I'll try and break this down a bit from my experiences (and hearsay) for you though.
Elemental is supposed to be the better rogue gear (Stormshroud). All elemental gear requires farming of some ridiculous drops off of elementals. They seem to be lowering how much you need for each item (they have lowered the requirements to make Helm of Fire recently) but it's still a lot of hit and miss farming. In addition to that, many rogues (including myself) feel like the Devilsaur set in Tribal is actually better than the Stormshroud set.
Tribal is supposed to be good druid gear, but it also does have the aforementioned Devilsaur. In my opinion, if you're looking to make money with leatherworking then Devilsaur gear is probably where it's at. You won't break the bank, but you can sell each piece for 50-60 gold. Devilsaur Leather is the only difficult ingredient in those (8 for gauntlets, 14 for leggings) but you and a friend could farm enough for 2 pieces in a couple of hours probably. They also need a boatload of rugged, but that's easy enough to buy or farm.
Dragonscale is the red-headed stepchild of leatherworking atm. You hear a LOT of complaints from those that chose Dragonscale about how difficult it is to farm the necessary components and you also don't hear anybody looking for certain Dragonscale pieces. I'm sure they sell when on the AH, but there's not people actively asking to buy them in public channels. My guess is that Dragonscale will be the first of the LW trades to be improved, although all 3 branches need it.