Minecraft wiki entry for Diamonds, associated text: In order to get Fortune III on an iron or diamond pickaxe the player need to consume much experience points per attempt, so a mob farm is handy for accumulating XP. While advanced methods are possible, it's fairly easy to build the experience by simply camping at a suitably modified dungeon. It should be noted that other things give players experience too; between mining, breeding animals, and fishing, a player might well get to level 30 or higher by the time they've built a table. The player also needs a fair bit of lapis lazuli, 3 pieces for the "final" attempt, and from 1 to 3 pieces for each try at resetting the enchanting table.