Gevlon, the Greedy Goblin has an interesting post up in which he explains how to make 1,000 gold a day by selling glyphs. Only problem with the advice was that I tried it, and it didn't work on my server. The materials (herbs or pigments or inks) just aren't as cheap on my server as on Gevlon's. And there is a lot more competition on the glyph selling side, driving the prices and thus profits down. I'm not saying his advice is bad, it is just not working for every faction on every server.
In another example I've been making good money by buying cheap Spellweave, Moonshroud, and Ebonweave for around 150 gold each, turning 8 of them plus other materials worth around 200 gold into epic robes, and selling those robes for up to 2,200 gold. Minus AH fees that comes out to up to 700 gold profit per item. But after having sold a couple, one or two other people had the same idea, so the prices for the cloth shot up, and the prices for the epics went down. So this is another idea which *might* work for you to, but isn't guaranteed to.
A major part of that equation is market size. Demand for epics worth over 2,000 gold is limited. Demand for glyphs is also limited, because people just don't change glyphs all that often. Other parts of the market are far more liquid, for example herbs/potions, ore/gems, or regular cloth. A single inscriber can crash the market for glyphs, but a single jewelcrafter won't crash the market for gems. And of course market size also depends on what faction you are playing on what server. On my server there are twice as many Alliance than Horde, and it shows in the AHs (which is why I have to use my Alliance bank toon sometimes to buy stuff for my Horde characters). Less populated servers have less liquid markets than more populated servers.
Small, illiquid markets can be both a problem and an opportunity. If there is only 1 item of a given good is sold per week, and several people try to sell one, they end up underbidding each other to the point where there is no more profit to be made. Some guy just decided to make 10 Spellweave Robes to level up tailoring, and you can forget that market for a month. The opportunity is that if a certain item doesn't sell very often, there is a good chance that many people long gave up on it, and that there is currently nobody selling one. If you are the only seller, you can dictate the price, within limits.
So "how to get rich quick" advice for World of Warcraft is rarely valid everywhere. A few people on your server having read the same market advice can completely spoil your profit. Big, liquid markets are more stable against such perturbations, but small, illiquid markets have their own opportunities. You just need to find them for yourself.