First of all: level up your First Aid to 325 right now, because I've got three words for you: Heavy Netherweave Bandage. Think all that they'll do is heal you? Think again -- they vendor in the game for a whopping 6g per stack, so every time you log on your AH alt, the first thing you should do is run to the Auctioneer and buy up all the Netherweave cloth you can find for less than 3g -- crafted up into bandages, each stack of cloth is worth at least that, so anything you buy for less than 3g (I've seen it as low as 1g 50s -- people are throwing away money) is pure profit. This is the biggest moneymaker I've found (you don't make much per stack, but after you've "processed" a few hundred stacks, the money adds up), and it made me regret selling Netherweave for anything less than 3g before I figured this out.
Second big tip: don't ever buy anything on the weekends. Ever. Prices soar on the weekends, so much so that you'll often be able to take advantage of huge bargains during the week, and then turn around and craft or just resell those items on the weekends, when everyone else is playing. I know you really, really want that Primal Air on Sunday so you can finish off your profession leveling, but wait three days -- by Wednesday, all of the AH sellers will have seen their auctions expired and will be ready to lower the price.
Finally: raw materials own all. The best thing professions in the game are for (not including Enchanting -- I believe that Disenchanting is the best money-making profession in the game, as even low level enchanting mats sell for lots on the weekends) is to make your own gear, since everyone and their brother has a guildie who can make them that BS chestplate or a leatherworking quiver. Costs of making items are negligible, but the costs of the raw items are where you'll make money. The one place crafting will help you is to make bigger and better raw items: I was able to buy up Knothide Leather Scraps like crazy on my realm's AH, and turn them into much more expensive Heavy Knothide Leather (although the stuff I could make with Heavy Knothide Leather barely sold for more than the mats -- I had to do a lot of price checking to make sure I wasn't overspending on things I couldn't sell later). Likewise, miners have it made, since people will pay more for bars than ores, even though the bars themselves are still raw mats. In short: use crafting to your advantage to make rarer raw materials, but don't bother crafting the actual items yourself if you want money -- people won't pay you to make something when their friend's alt will do it for them for free.
A lot of this stuff is common sense once you've been working with the AH for a while (and since every realm is different, working the AH on your own realm, day in and day out, is the best way to keep track of where prices are and what sells best). But just in case you haven't had the experience of squeezing a nice chunk of gold out of the AH yet, that's what I learned in my run up to an epic mount. Nowadays, I just do it by habit -- there's nothing I really need to buy anymore, and daily quests give me more gold than I really need. But there's a lot of fun to be had, and money to be made, in following the wacky world of AH pricing.