The number one rule that you should have in any game with an economy, and has been stated as the rule of thumb:"Buy Low, Sell High."

World of Warcraft has several occupations that have a high demand from other players. Herbalism, Skinning, Mining all can make a profit in selling the raw materials for Alchemist, Leather Workers, Blacksmith/Jewel Crafters etc...

Then there are the Crafters (I know I know Maddux )
Blacksmithing is the bottom of the rung, because no one really wants to buy weapons/armor since they have so many better mob drops from dungeons. Not to mention the materials for them are generally way to high to profit off of. The same goes for leather workers. But, if you have a enchanter as one of your characters, you can make the items on your blacksmith/leatherworker/tailor and send them to him to disenchant. The mats from disenchanting usually give off a high resale value. Alchemist on the other hand, have cheap mats and the resale for elixirs and potions is quite high, as many low and high level raiders live off potions. I've been told for many high level raids, if you don't have a flask on your buff bar, you wont be taken on the raid. Also, depending on what specialiaty you choose, you also have a chance of making multiples of a potion/elixir/transmute you make, thus raising your profit signifintly.

My last thought, which goes in hand with my motto. Look for resale deals on the AH. There have been many times when I have seen rare or epic items that have been put on the Auction House for a tenth of what they are worth, then have been bought and resold for a much higher price. In fact, I just bought a trinket for 60 gold that has a resale value of 1200 i.e.

So there you have it, my take on the best way to make money in Wow. Hope you all enjoy it and that it makes sense. Remeber my motto, "Buy Low, Sell High!"