I need to mine a lot, and I mean A LOT of diamonds. What is the most efficient way to do so?
It is to strip mine on y-axis 11 with a good pickaxe.
First, have a diamond pickaxe with at least efficiency III and Fortune III on it.
Fortune III is good because it gives you much more than you mined: 40% chance of getting 1x what you mined
20% chance of getting 2x what you mined
20% chance of getting 3x what you mined
20% chance of getting 4x what you mined
So, if you mined 10 diamond blocks, you would get about 20-30 diamonds.
Efficiency is very important in mining quickly and fast. It really helps save your time.
Go to y-axis 11 to find the most diamonds and rare items. Although some people say 12, I tried out 11 and it works better. It is your personal preference.
Lastly, strip mining. Strip mining is first mining a straight tunnel and on each side, every 3 blocks start a new tunnel.
This is a birds-eye view of a strip mine
Remember, spend a lot of time doing this and you'll have stacks in no time!