I used to think that making gold in WoW was hard, but I quickly realized that it is just like in the real world, a mixture of effort and opportunity.
Making gold in WoW is not hard at all, there are various ways of doing it. It is a little of auction house play, lots of smart expending and well, questing or raiding.
You need to think of one of your toons as a work horse. If you only have one, then guess what one of its purposes is. I have found that the most lucrative of professions in WotLK is mining. Why mining? because of Elementals and Ore. The prices on those two things are always pretty consistent.
As far as crafting professions making you good consistent money, jewelcrafting is pretty excellent. So if you are just starting in the gold making business, a Miner-JC would be the way that I would go.
So how to go about it?
Quest, Quest and then quest some more. Reason being that while questing you will find the good spots to mine what you need. While add ons are there to help out with this process, and you can look up the information online pretty easy, questing will show you the best routes for mining. That and killing mobs will get you drops that you can then turn around and sell in the auction house.
I do think a must have addon is auctioneer. It will help you decide quickly what you want to sell your stuff for.
There is really no excuse for being broke while playing this game if you are top level (right now 80). There are plenty of daily quests that will give you 10g. About an hour of dailies will make you 100g.
Now that I have told you the basics of making money, the key is how to make more and my answer is SAVE. Do not buy an upgrade to your gear as much as you are itching to. Save all your money until you have EPIC flying. Once you can move fast through the world, your money making will get tons easier and grinding will yield lots more.
So this is my 5 minute guide to becoming WOW RICH