Players who make a lot of gold do it by knowing their server economies inside out and exploiting any gaps.
There's no real secret, use auctioneer, flip things for higher prices, use whatever professions you have, it all adds up. Best advice I can give you is to really get to know how your server works, familiarise yourself with the Undermine Journal, run a bunch of AH scans, places where you can make gold should jump out at you.