Based off of vanilla minecraft, best bet is to go to a desert, savannah or mesa biome, and have an efficiency V pickaxe. Press F3 to see what your coordinates are and head down to Y=5-12, because diamonds are more common around there. Grab a water bucket with you incase you have any accidents involving lava, and dig away. You’ll be showering in diamonds in no time. However if we are talking about most efficient way without caring about cheating, an xray texture pack/mod is definitely the fastest way – possibly even an auto mine mod. But I still believe the more enjoyable experience is the first method I mentioned.
Although the most efficient way to mine diamonds on minecraft would be using a diamond or iron pickaxe. Truthfully, who knows what the most efficient way is? I think that’s part of the fun of Minecraft! there is no one way to correctly play the game. Everyone is going to have a unique and special way they play the game, and that’s awesome! For me the best way to mining diamonds is put on headphones listen to my favorite podcast or music and just grind out those precious, precious diamonds. If I had to chose a second best way I would say that nothing is more fun then staying up late mining with your friends, and its moments like that, that make me keep coming back to the game.
Alternatively, just dig down to y-axis 11. Then, start mining in a random direction. Eventually, you will find diamonds.