Focus on a specific item
Do not do this one too often since it will take a lot of time away from leveling to get going. You will have to watch the market for about a week or so to get accurate Auctioneer data and you can lose Mortal online gold as quickly as make it. Just focus on a specific item and watch the prices like a hawk and buy when it is low and sell when it is high. Easier said than done, I know. It does take practice but practice makes perfect.