Pro-tip #1: Placing items on the AH at the right times can mean the difference of 10-20g per item. Best time to load the AH up is just before raid time. All the happy looters come to gem up their tiers and will pay any price to do it. If you time it too soon the under-cutters will get you.
Pro-tip #2 Only place a maximum of three of the same items on the AH at anytime. Keep the rest as stock in your bags or bank. Scarcity drives up cost. If two items sell, put up two more.
Pro-tip #3 Work the corner. Cut gems for people, many 2g tips add up to big bucks.
Buy raw gems or proespect ore.
Sell Cut gems.
You get more if you have recipe's that are harder to come by like the world drop cut recipes.
The vast majority of the gems on the AH on my real go for only about 2 to 7 gold each. Ore sells for more than that.
I know because over the past few months I saved up nearly two hundred gems and sold the majority of them after I cut them on the AH for that amount. Only one type of gem went for about 80g. And that was a perfect cut.
if you have an enchanter friend or alt, 2 primal earth will make you http://www.wowhead.com/?item=43248 which you can make a killing off of by dusting. if you can even buy primal earth at 6g a pop you'll make a good bit of money. i managed to pay for my epic flyer just by working the AH for primal earth, then selling stacks of dust. this is also a good way to get cheap enchanting mats if you dont want to sell them.
-Never waste your time cutting gems except for friends/guildies.
-Post gems on the AH, make rings to DE if you have an enchanter and profit.
-Do the JC daily every day if you can.
-Check to see how the demand is for the different epic rings and save up JC tokens to get 1-2 designs as these can be fairly profitable as well. Often you'll want one or 2 types for yourself anyway(if you're a hybrid class or have alts), might as well try and make some gold while you gear your toons.