1. Mine at layer 12, but always bring a water bucket. (The reason is that the probability of a diamond spawning on layer 12 is the highest.)

2. Create a branch mine. (For me, branch mines have been the most effective way to find diamonds.)

3. When you find redstone, create passageways on every wall, 2 or 3 wide, and mine until you have reached 30 blocks or until you find diamond. (The reason for this is that I have found that redstone usually indicates that there are diamonds nearby.)

4. Once you have mined a diamond vein, always check around it. There is a chance there might have been an extra ore that just isn't visible.

5. If you find a large lava pool, pour water over the lava then always check around it. There is a large chance diamonds will spawn close to lava, and the bigger the pool, the more lava there is for diamonds to spawn near!

6. Mine every ore. Diamond can spawn next to anything, so there's a chance you could be mining an iron ore and then find diamond. If you hadn't mined the ore, you would've never found the diamond!

7. Be patient and realize that diamond is the least common gem/ore in the game. These tips help, but time and persistence are the most helpful way to find diamond.