A beautiful sand island is the place where you spawn. This destination is near a birch forest biome. Dig down as deep as possible to get the diamonds.
Pay attention to the following image. It tells you where to dig exactly.
Follow the instruction of this image to know how to dig down.
It requires you a lot of effort to dig the sand and find out the diamonds.
Avoid falling into the lava. This is because the diamonds are above the lava one block.
As a result, you should choose Four Diamonds Under Spawn Seed to get the diamonds immediately.
Seed: chocolate for days