Ok I know you guys have heared this probably hundreds of times but the auction house is by far the best way to make gold. There is a addon you well need that you can get here:
Auctioneer | World of Warcraft Addons | World of Warcraft @ Curse.com
Ounce you downloaded auctioneer and extracted it to your addons folder log onto wow make sure you turned addons on..
Go to the auction house and click "Scan" ounce the auction house is scanned just click search
You are not searching for a certain item. Ounce you hit search click PCT it is on the top right.
Now that you hit PCT you well notice percentages on the side, make sure you make it so it is the lowest percents to highest.
Some percents are blue others are green, then yellow. Only buy blue.
If you notice, blue is 50% and under green is 50-60 yell is 60+ or so. It is time to go sticker shoping. 50% means it is 50% off, 60 means 40% off etc. Just buy stuff that is 50% of or so.. and then post it for higher.
My friend made 6000G doing this for about a 2 weeks, he only logged on like a hour a day.
It was hard explaining this with out pics, I don't have a a wow account ATM.
Hope this helps.