Lately, I've really been pushing hard to get the 5k gold for my epic riding skill-- as I said on Friday, that Netherwing mount is calling my name. And so, on the advice of a rich guildie, I've finally made it a point to get a fulltime auction house alt. I chose one of my younger, less-played alts, stuck him between an Auction House and a mailbox (it happened to be in Thunder Bluff, but it could have been in any capital city), and made it a point to start scanning the AH every day, posting auctions when I start playing, and sending items to the alt when I'm done playing. That way, the next day when I log in with my bank alt, all those items are sitting in the mailbox, waiting for me to put them on AH-- right after I scan it again.
That's what Amanna at Adventures in Azeroth does as well-- though she goes even farther and looks for deals on gear she has in mind to buy. It would be great to have that kind of know-how, and I'm sure it makes money, but I don't have time to know the approximate costs of every little thing-- I leave that to Auctioneer. (Auctioneer does come with a mod called Bottomscanner (used to be called Bottomfeeder) that is supposed to find deals on high-priced items for you, but I'm not sure that I can get it to work right-- I'm worried that I'll spend a bunch of money on an item I can't sell).
But if nothing else, I do have to agree that the formula works-- check the AH with your alt when you log on, and mail items back to that alt when you're done playing for the night. It's a basic thing to do (and anyone who's been interested in making money before has probably already started doing it). But making money seemed like such a chore before (I'd rather be killing stuff or grouping up then worrying about prices and checking the mail), but it's actually become fun for me to log in every day and check what's sold and how much gold I've earned.