This seed allowed me to find diamonds in minutes! It's either Loot or Loot!
Step 1: Step One
Open the Advanced Settings, and set the world type to Infinite.
Step 2: Step Two
Put in one of the two seeds above in the intro.
Step 3: Step Three
When you spawn into the world, look around for a cliff in the sand. You should be on a small island. (If you aren't on an island, try the other seed.)
Step 4: Step Four
Gather some wood and set up shop in the cave.
Step 5: Step Five
Enter the cave through the waterfall. Find some iron to smelt, and save the wood and stone picks for destroying stone, coal, and iron.
Step 6: Step Six
Keep exploring the cave while being careful of lava to find 11 diamonds (that's how many I found.)! Hope this helped!