You need 3 things: Knowledge, Time and Luck.
We've already been through Knowledge in the previous post.
Time, as they say, is of the essence.
The most important part about the Time factor is how much of your own playing time you are willing to spend at attempting to make gold. Because some times you can spend your entire daily playing time strictly managing your items, shuffling them from character to character, transforming them, crafting them, browsing the Auction House, calculating, posting the items... Suddenly it's time to go to sleep and you haven't spent any time working on your main character!
That type of decision can go hand in hand with the type of auctioneering you're willing to delve into, because managing 200+ auctions can take a lot of time, compared to 20+ auctions that you will keep posting until they sell.
The proper timing at which you post your items will highly influence your chances of finding buyers.
Other blogs have been experimenting with that fact, of course, and have come to the conclusion that the quickest buying times are when servers are around their peak times - and that's when a dedicated gold-maker will be in action. That means browsing the AH for open markets, buying out the competition, canceling and re-posting auctions, etc.
Basically: making sure that people with the gold get what they demand, and you are on the front lines with the goodies.
Your auctions will be usually set to 12 hours for max profit, because if the market becomes hot there's no need for you to keep your items up there while it keeps being undercut and left for dead until the auction expires.
Mostly everybody has gone to sleep, some farmers will start their rounds, and the people that browse the AH are few... and you have gold-makers on the prowl for profit.
Usually, a lot of auctions will be lingering until their expiry time and not a lot of people will impulse buy.
What you'll find is that - while you have the odd-scheduled person using the AH for normal needs - gold-makers will be running their auction scan addons and will peruse their results for anything mathematically profitable. That's when items that don't seem attractive to most players will sell, only to be put back on the AH at a higher price (or transformed or crafted, etc.).
That's the wasteland where auctions set for 48 hours will rule above all and you can take advantage of the fact that all the best deals have been bought and you can sneak in your items, should you make them desirable enough.
So, as you have probably gathered, off time sells are either strategically planned or a big gamble.
Which leads us to our 3rd factor...
The Auction House is a game replica of the stock markets. And no one can determine the exact way and time the markets will rise or crash or wobble. But one thing's for sure: sometimes people get lucky.
You can't determine with 100% certainty what the needs and means of everyone are on your server.
Otherwise, everyone would be either all rich or all poor.
So sometimes you'll get people buying everything that you are selling.
Maybe they think they've made a good deal.
Maybe they think your prices are too low and they want to resell at 300% profit.
Maybe they really really need those items right now and can't be bothered to look at the information about that item. They don't know the drop rate or where to farm it, or they are going to their nightly raid in 5 mins and are buying your items in a hurry no matter what the price is.
Maybe they mis-clicked Bid or Buy (even if there's a confirmation window that pops-up right after, it still happens!)
Maybe you're the only one selling the item.
Maybe you're the only one with the most reasonable prices.
It happened to me several times that I've been taking a serious gamble with some items and have come back quite surprised that they either sold or they've sold almost immediately after I've posted them.
The fact is: Luck happens.
You can't count on it to happen, but when it does you become very happy about it.
So there you go: the 3 main factors that determine if you become successful at gold-making.
Make them work for you and you'll find yourself wealthier than you were before!