The lights are on
First, dig a spiral staircase down to bedrock but be careful not to fall into lava--don't dig straight down. Make sure you bring a cobblestone and an IRON pickaxe because a golden one doesn't mine diamonds. When you hit bedrock, branch out your tunnel. If you have the PC version, you have a slim chance to find diamonds in a chest in a village, stronghold, near a mob spawner, or in a mine shaft (if there are more places someone please tell me). The trading system as of PC version 2.5 allows you to get diamonds too (if not, tell me). Also, always take the deeper tunnels in caves.
Edit By: Mayabearr
Tuesday November 8, 2012 10:45 PM
Diamonds spawn relatively randomly so there isn't much of a method to finding them. The best advice I could give is through my little experience with actually finding diamonds. Normally I tend to find them near underground lava. Make sure you have an iron pickaxe (not a golden one as that will not mine it) and do not, I repeat DO NOT dig straight down. You'll probably fall into a cave or lava and we don't want that do we?
The best way to dig around is to dig in a stairway type way at the top and make it four blocks across. When you get bored or tired of doing that, mine a giant room for yourself in that general area. When the time comes, you can just start digging the same way as before. Note: This does get tedious after a certain amount of time, but is very worth it once you find the diamonds.