I think Bossland made a long long post about this subject a few years ago, you can begin there.
But the prices atm. are very hard to compete against proffesional sellers. a Protip would be to start small, i come from Denmark and started to sell to my friends in my guild. Now my friends have said to their friends they could just contant me whenever they needed gold. Im a known name in the industry now(somewhat i think atleast).
I wont give you all of my secrets, but a very good tip is to not overflood the AH. Something i did till roughly a month ago was have 10 bots running Black Temple, but i found other ways to achieve gold, that i like more. (the BT way is very good, hard to track, aint other people, etc.)
Also, as a long-term investment, it's not worth using public profiles(even tho i released some of mine to the public >_>). I also think it was mentioned earlier that point, but wanted to be sure.
anyways GL dude.