After a few weeks of collecting data in the Market Watcher addon, I finally have some decent charts for the WoW Index. The great thing about taking a look at this kind of data is to see when it's best to buy, sell and farm. Looking at Saronite ore, we can see that weekends are definitely the best time to either farm if you can, or buy and prospect for gems. Another thing the graphs show is that since the patch and Arena season 6, the demand for Infinite dust and Dragonfin has gone up at a steady and moderate rate.
If you're having trouble figuring out what day is best to sell or buy or what to focus on during the weekend, install Market Watcher and scan every day until you get a good 2 weeks worth of data. Being able to visualize what's happening with a market can be a great way to figure out what to do.