If you do try to play the ah start out small and work up. buy and repost some of the pre bc gems or enchanting mats at higher prices stuff like that. (just 5-10 different items to start out) you may get burned on an item or 2 but you slowly start finding out what you can control and what you can't. Over time you let your list grow and eventually you are turning a decent profit every day.
I also recommend making a spread sheet listing the maximum price you bought the items for. (so you don't make a mistake and resell for less later) As your list grows this becomes more and more important.