First off, when you want to make big money with the auction-house be sure that you scan the AH pretty often with auctioneer. I was able to make almost 15k gold within a week.
Just invested 2k gold, bought every available damn frostlotus during the week and sold it at friday night. People go nuts for flasks in their raids.

So just scan the AH and be patient for some bargains. Don't bother with dumpers and don't even try to underbid them. Buy their stuff and sell it at your price.
For starters, just try to watch out for frostlotus and arctic fur. Sell them in different stack-sizes. You should be able to gain some nice cash within a few days.
(I'm using different toons to sell the items. So i can upraise my own prices and let the high prices look like bargains.)

When you feel comfortable with this kind of trading, start aiming for higher prices. Take a look at the inscription-cards. Maybe you can buy the cards for the Darkmoon-Cardset: Greatness. (This set runs for about 10k gold @buyout on my server.)


Also, i had fun while farming herbs straight for 2 weeks. Send all the herbs to my inscription-char and made glyphes (and sold the frostlotus). Just had to wait till they announce the release-date. Made every damn glyph 5x and gave them to my trading-char. So i just had to dump all glyphes to the AH a couple of days before that patch.

If you can spare 2k gold to try out trading, just give it a try. (Be aware that your gold also can be lost.)

Currently i would be able buy "Reins of the Traveler's Tundra Mammoth" for my first team. Since my first team isn't 80 yet I save the gold to get them some nice gear.