I highly recommend actually staying in the 20-60 range zones until you ding 62. The reason for this is that despite getting a slight penalty in experience for being over-level, the advantage of having flight will more than offset this. That, and WOTLK and TBC zones are the slowest part of the leveling process. Minimizing your time there as much as possible is worthwhile.
Make sure you have the two Flight-Path toys purchased, as this can save you time. It won't have EVERY flight path, but will have major locations for faster travel if you need to switch zones entirely(which you will). If you buy the toys on one faction, it unlocks for the other faction as well. So don't spend double the gold! These toys can be found at the heirloom vendor(Undercity for Horde, Ironforge for Alliance)
101+ At this point you'll start taking a penalty on quest/bonus objective experience for every level past 100. Treasures, however, remain worth their full value all the way through level 105, at which point they'll be worth something like 15% less, and then another 15% more when you ding 106. I recommend that you stop questing/gathering entirely, and collect all the treasures you can stomach, only avoiding any annoying to reach ones inside caves or behind elites/rares(where scaling does bizarro things).
My second least-favorite part: leveling ranges. Zones are divided into leveling ranges; some are for levels 10-60, others for levels 58-80, and so on. On the surface, that appears to make sense; while there are odd moments where you're presented with the content from two expansions at once, it does mean that you're more or less going through content in order, at least by expansion if not by level.
There are professions you can train in to make money in the game. You can be an herbalist to pick useful plants; an alchemist to make potions; a miner to mine ore; a blacksmith to craft armor; a jewelcrafter, who can cut gems that can be socketed into certain items to augment them; or an enchanter, who can enchant items to have bonus stats or effects.
Some players like to try to game the auction house to make gold by buying things for low prices and crafting them into more valuable things, or simply reselling them at higher prices. You can also use large amounts of gold to buy special luxury items like very expensive vendor mounts that carry portable auction houses and repair vendors. Sometimes you can find special mounts that were exclusive to the Warcraft collectible trading card game that was discontinued in 2013, though many of the most desirable ones, like the Spectral Tiger and the Giant Rooster, are very rarely sold on most servers, and go for the maximum price of 10 million gold.
For future reference, it is a great option to purchase mounts and pets as a long-term investment. Not only do their prices scale well even when a new expansion drops, but there is always a demand for them. The only drawback to this strategy is you would need a hefty amount of initial wow gold investment and also maybe have to go through the motions of spending for a guild bank.
I remember time when I was at teenage and I used to spend real money for wow gold from some suspicious "hacker" site from China or Korean what ever(note: I didnt spend much). And now I have realized how foolishly I did even I didnt about real money problems in there. Now that I have grown up I have also realized that I was one of those that caused playing problems for those young boys, that they had to play like 24/7 to farm gold for us lazy people.
There are also numerous gold-making guides available for World of Warcraft players. Currently mmobux recommends Killer Guides' World of Warcraft Gold Guide, which covers a broad range from daily quests and professions to making gold while leveling and auction house trading. 'Standard' farming spots are covered as well, making it an interesting resource for bots as well. Yielding up to 500 gold per hour, the strategies are suitable for players of all skill levels. If Killer Guides keeps the guide up to date, it probably will become a valuable resource for professional farmers as well. There also seems to be a German-language version available: WoW Gold Guide (German)