The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul). The guides have been tweaked many times over the years to make things "faster". The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms. I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
Swamp Jaguars - Western part of the Swamp of Sorrows is inhabited by deadly feline species, the Swamp Jaguar. These big cats drop a lot of Vendor Trash Items (Long Soft Tail and Bristly Whisker), Large Fangs (used in Leatherworking, Blacksmithing, and Alchemy Recipes), Wicked Claws (used in Leatherworking and Blacksmithing Recipes), 12 Slot Bags, and most importantly can be Skinned for Heavy Leather and Thick Leather (Skinning is not necessary for this spot, because of Jaguar's already great loot table). This is one of the best spots for farming your Level 40 Mount Gold. Recommended level - 35+ (you might need to clear other Swamp creatures as well, just to be safe).
Learn only the Essential Skills - Learning new and upgraded Skills gets very expensive very quickly (Buying a single skill that requires level 30 will cost you 1 Gold, and a single level 40 Skill costs 2 Gold) If you buy just the essentials, you can save anywhere from 15 to 30 gold before level 40, depending on your Class. Generally, higher ranks of skills that are used for their utility effects can be skipped (these include Warrior's Harmstring, Rogue's Gouge and Kick, Mage's Frost Nova, and many other CC and utility skills and abilities). Also, don't buy any ranks of abilities that you will not use during leveling (things like Rogue's Expose Armor, Hunter's Eyes of the Beast, Warlock's Eye of Kilrogg, and so on).
Kaivax, a WoW forum community manager, revealed that WoW Classic's class design, battleground mechanics and stats on existing items will be set to their 1.12 state, despite the game releasing content that expands beyond that. This removes "progressive itemization," so if the stats on a specific piece of equipment was changed during the original updates, that won't take effect in this version.
World of Warcraft is very old, by videogame standards. It was released in 2004. And about every two years, Blizzard releases a new expansion to update the game. Typically expansions don't really replace content, but it does displace it, and changes to mechanics and player abilities are indeed permanent and "retroactive". And in 2010, the Cataclysm expansion DID actually replace the old content from the release game.
Check Item's Vendor Price before posting it on the Auction House - Selling items on the Auction House below their Vendor value is a common mistake. Avoid it like fire, and always make sure that you are not losing Gold on your Auctions. If you plan to sell an item on the AH for a price just a tiny bit higher than its Vendor value, you might be better off just vendoring the said item (this will allow you to avoid the risk of losing an Auction fee if your Item doesn't sell).