You can find the diamonds easily not just randomly, follow the simple steps below

Make sure to have a lot of torches (more than 100), have a pickaxe (a stone one when starting the mine, iron if you can), and weapons and armor, in case there are mods in caves).

Make a staircase that goes down. To make this, make a 3 block high hole, make the same hole that starts at the middle of the hole to one block below the lowest block of the original hole, and repeat. Keep doing this with a pickaxe, and it is advised that you come back every 10 minutes or so to get more food, store goods in chests, and make more picks and swords, etc.

Once you reach bedrock, dig around, and find the bottom-most layer. That is layer 0.

Go up to layer 15 (1 block is 1 layer), and make a small room there. Make chests, a crafting table, and a furnace, so you do not have to go all the way up to your home to craft more tools.

Make a several pathways leading out of the room, 3 blocks apart. Then tunnel your way through the pathway.

If you reach a cave, or you reach a satisfying point, dig 3 blocks to the tunnel next to the one your in, so when you reach that point in the other tunnel, you will know.

Finding diamonds are rare, as they only spawn a rate of 0.10% for layers 15 and 16. So don’t give up, and keep mining!

Note

• A huge mistake in mining is not using iron pickaxes. You will find a lot of iron on the way, and iron will speed up the process.
• Texture packs rarely find you diamonds, as they can only show you blocks that show their surface. Use a diamond finding mod, but finding it legit will make you feel more proud when you find the diamond.
• The world record for finding diamonds the fastest in a natural seed is probably 2 minutes, set by ant venom on youtube, though that is not in the Guinness world records, as the world you spawn in may be a one with diamond at least 5 kilometres away from you, which makes you at a disadvantage.
• Also have a bucket of water on you, in case you catch on fire, by lava.
• Never dig straight down, unless youre attempting a diamond finding record, as lava may be underneath you. Never dig straight up either.