This option is better to use at level 40+. Higher level you are is better, more money you make then. All you do is farming dungeons or specific bosses. Here you kill a few birds with one stone: you get lots of experience (make sure you have all quests in your quest log, always ask your teammates to share) if you are still leveling; improve your current gear; and loads of loot (clothes, recipes, even crappy grey items selling for a lot to a vendor). If you are in a group, think about your groupmates if they need an item or not, don’t roll need on everything.
To gain gold in World of Warcraft, you will primarily be grinding professions which are fantastic for receiving rewards. Mining is an example of a great profession at an early-game level. While Herbalism is actually the best gathering profession, the issue is it uses consumables which can make the profession rather costly, with the investment required.