How to make gold in Wrath of the Lich King is not that hard or different from the wow gold making strategies in other major zones of the game. You have to know what players are looking for in terms of basic crafting materials and make sure you ship a steady supply to the Auction House.
   As the primary gathering professions you have like Mining, Herbalism or Skinning then you'll be in a good position to farm these materials during the course of your questing and make a ton of gold. This assumes that you have at least reached a profession skill of 350 and have been trained to Grand Master level. Trainers can be found in the two starter areas of Borean Tundra and Howling Fjord.
   Still, you are away a little off your profession skill level you can still gather Frostweave Cloth from the many humanoids of Northrend and Meat from the large selection of animals that roam there. Meat and Cloth are still good gold making strategies at this stage in the game and often overlooked as a good income source by many players.
For the most part, it helps if you combine questing with grinding and gathering. Not only will you level faster but make enough gold in the process to ensure a down payment on that Woolly Mammoth you've had your eye on in the Dalaran market place.
Take this as example, in Kamagua the island connected to the Howling Fjord by the Ancient Lift. There was the quest 'Feeding the Survivors' from Elder Atuik of the Tuskarr. The quest calls for the gathering of 6 Island Shoveltusk Meat from the surrounding Shoveltusks (don't leave the island). These are also being attacked by wolves. In the course of the quest you'll end up killing many Shoveltusks and the attacking Wolves.
It is easy to get this quest and you do not have to travel far from the quest giver. In the course of completing the quest, you'll also end up with a stack of Shoveltusk Flank in addition to some Worg Haunch. These sells very well on my server (but check your server for pricing) and are in demand from players wanting to level their cooking and complete cooking quests. As a bonus to the XP's that you'll get from the quest and kills, you'll earn reputation with the The Kalu'ak.
When you are making a decision to leave the warmer climates of Azeroth for the frozen lands of Northrend, you'll have to make sure that your bags have plenty of world of warcraft gold, for it turns out that battling the Scourge is an expensive business in the land of snow and ice.
In the Burning Crusade, it matters not if you bought your epic flying mount, you'll still have to level to 77 and then fork out 1000g for Cold Weather Flying before you can gain the freedom of the frigid Northrend skies. So it will help if you hone up on your gold making skills early on in the game so that you'll have enough to at least pay your bar bill at Valliance Keep.