Don't go finding diamonds before doing this. (Unless you need to get diamonds so you can craft the diamond pickaxe. ;)

1. Make sure you are at level 48-50.
2. Find 3 diamonds and craft a diamond pickaxe.
3. Make sure you have an enchantment table with bookshelves.
5. Exit minecraft, and go to your minecraft world save folder.
6. Make a copy of your world on your desktop.
7. Open minecraft, enchant your diamond pickaxe when you see levels 48-50.
8. BE PATIENT.
9. When you enchant it, make sure your diamond pickaxe has Fortune III, if it doesn't then exit minecraft and delete your world, copy your backup and paste into the minecraft saves folder.
10. Keep doing it until you get Fortune III.
11. When you do, carry it with you at all times when going diamond hunting.
12. You can also use the copy and paste technique before mining diamonds with your enchanted Fotune III diamond pickaxe to get four diamonds for each block of diamonds you find instead of it having the probability of it dropping only one diamond.

I recommend strip mining to easily find diamonds. (: