If you are serious about making gold on World of Warcraft, then it is important that you pick the right professions and the right times to take advantage of people. By doing this it is extremely simple to have more gold than you know what to do with.
To do this you have to break a World of Warcraft into it's three main pieces, the start, the middle, and the end. Every part has big opportunities for making big gold.
Start of the Expansion
It is not hard to figure out that the best time to make WoW gold is at the beginning of an expansion. I made 40,000 gold in the first few hours of the Mists of Pandaria expansion, and why? Because I farmed.
At the beginning of an expansion, throw your hopes of server first anything to the wind and neglect leveling. Just get out to that new zone and farm like crazy. This is the time when people with money are going to spend that money to powerlevel their professions to try for that server first.
Go out there on your character and farm crafting materials. This means farming herbs, ore, gems, leather, fish, enchanting mats, cooking materials, and inks. It honestly does not matter what you farm in the first day of the expansion. Anything will sell for an exorbitant amount.
Though the first few days of the expansion are a skinners wet dream. This is the easiest way to get money quickly as people are killing skinnable creatures as fast as they spawn for quests. This means as long as they are looting the corpses you can follow people around and skin their kills.
As the expansion goes on, ore prices are the first to drop down. So you may want to consider farming ore before all other crafting materials. As ore goes down, so do uncut gem prices, just be aware of that.
The most stable crafting materials are herbs and skins. Herb prices stay fairly high for several weeks then equalize around the middle of an expansion. Skins for some reason, are always in demand. I am certain it is because Leatherworkers need a lot of leather, but do not want to go get it.
If you still want to level and gather as you go, then some other viable options are to sell all your bind on equip greens. Enchanters with money love to buy these up to disenchant for enchanting mats. Also there are a few people who will buy them as upgrades as well.
While you are out there leveling, you can also sell any meat you find. These meats are most likely cooking ingredients and will sell spectacularly in the first few months as raids make food and feasts.
Middle of the Expansion
The middle of the expansion is where your farming efforts still pay off, but not nearly as much. People have powerlevelled their professions and are now working towards getting raid ready.
Now instead of crafting materials, it is time to start selling things like flasks, food, enchants and cut gems. Those four things are essential to raiders and will sell quickly at a decent price. This is also the prime time for another fun thing.
Every expansion brings new darkmoon cards that can be made by the Inscription profession. I will not lie, this is how I made most of my money. The first darkmoon faire of the year is when everyone starts doing their card trading. If you get a full deck of Aces through Eights, you can turn those cards into a deck. If you trade that deck in at the Darkmoon Faire, you get a trinket that is bind on equip.
The trinkets that you get from those cards are viable all the way through the end of the expansion, except for the tanking trinket, those are always crap. For example, I made my Tsunami card near the beginning of the Cataclysm expansion and used it right up till the end since the trinket that was good enough to replace it just would not drop out of the Dragon Soul raid for me.
Those trinkets sell for as high at 70,000 gold the first darkmoon faire week to around 30,000 gold the rest of the time. If you do not feel like trading with people for the cards you need, the cards sell for about 3,000 gold each on the auction house.
End of the Expansion
This is where it becomes hard to make any money. The expansion is near the end, people are bored with raiding and nobody seems to be buying anything. This is the part of the expansion where you should not bother with farming current crafting materials anymore.
So what does one do now?
The thing about the end of a World of warcraft expansion is that people are fighting getting bored with the game. This is where people focus on leveling alts. With people leveling alts, this means you now are going to farm low level crafting materials.
Low Level enchanting mats sell the best during this period because alts outlevel instances so fast that they have to buy the mats to level enchanting. Low Level ore sells good as well, especially thorium. this is because people need a lot of it and have no will to go to Un'goro Crater to go do so.
The harder to find herbs like Gold Clover sell nicely as well. Again, because people do not want to farm them.
The only thing that does not sell well is low level skins. Skinning is the easiest thing to level and there rarely a shortage of low level skins for leatherworkers.
there is a small niche market you can take advantage of too. It's level 15 gear, especially shields. Level 15 is when one can queue for Dungeon Finder and most people will buy the gear they need to be overpowered. Or sell rings or neck pieces for those that like to PvP.