The Minecraft Book
Video Tutorial Series- How to Find Diamonds
From YouTube user
Here’s a simple how to video with regard to finding diamonds. I agree with this chap that he got lucky in finding diamonds so quickly, but generally speaking, this is the way to do it. Sinking several mineshafts into various walls than having branches off those shafts is the way to reliably find diamonds. But make sure you don’t get lost.
To avoid getting lost, follow this tip: Place all torches on the wall to your right, not on the floor. Then, if you get turned around somehow, you will remember that going out from your base, all the torches on the walls are on the right side, so if you want to go back, simply make sure that all the torches are to your left, and follow the trail back.