Here's a quick 7 step guide to mining loads of diamonds:You'll need: Water bucket, pickaxe, sword, shovel, ladders, torches, food.Recommended: Armour, silk touch pick, fortune pick, axe, chest.1) Establish a base. A decent distance from spawn, so there are still diamonds, but not too far, since you have to transport everything back to town safely.2) Get to bedrock quickly. The fastest safe tunnel is 2x1. Alternate digging on the block you are not on top of, and be ready to fill the wall quickly in the odd case you encounter a lava pocket. The other worst case scenario is a ravine or huge cave, in which case use your water to descend safely. (Water puts out lava and also should flush away most mobs.) Never dig directly below you. Place ladders along one side as you drop so you can climb out easily.*3) You can see your level from the ground by pressing F3 (the Y coordinate.) Stop at about level 10, and mine a small room. Diamonds do not exist above level 16. I used to think level 12 was optimal, but then I went over my mines and dug down just two levels and there were loads of diamonds there.4) Fill in the last part of your shaft so it's 1x1, with the ladder out one block. You can safely jump all the way from the top, pressing against the wall opposite the ladder, and catching the ladder to get down quickly and safely.*5) How you construct your mineshafts are up to you, but keep in mind that a width between shafts less than 6 blocks apart is inefficient (there's a study on the wiki about it). Of course you wont get all the diamonds, but you'll get a high percentage of them and the world is infinite (whereas your time is not). You will encounter lava. Block it quickly, and mine over it, then douse it with water to create a nice obsidian room that sometimes has diamonds. Caves and dungeons can be explored up to level 16. Don't waste time going higher than you need to, and don't risk getting lost.6) I recommend keeping a spare chest, hidden or locked, with incomplete stacks of ores/resources. This way, you can ensure you carry back a full load each time. An ender chest is also useful to increase carrying capacity. If you constructed a safe nethertunnel, and stash your tools in the chest, you shouldn't even need a sword and can just bring back a full load of material each time.7) Upgrades. You can get 2.2 times as many diamonds with a fortune III pickaxe. (Same with coal, redstone, lapis, and emeralds). If you use a silk touch, you can get ores, which are often almost as valuable since people with fortune III pickaxes can resell the resources.Hope you enjoyed this guide and if there's anything else you think I should mention, please feel free to let me know.*Getting a lot of comments about step tunneling. Of course, step tunneling works as well, though it has many disadvantages: Advantages of using a vertical shaft:Reduced construction time. A step tunnel from height 64 to height 10 will require the removal of at least 3 blocks per level, or 162 blocks. Using the method above only requires removal of 108. This, of course, translates to reduced construction time. If you choose to construct a full stairway or give a bit of clearance, this increases to 216 blocks, with of course additional time in constructing the stairs themselves (which I find take a bit longer to place than ladders). If you choose to use the argument that more ores are exposed, this would be correct. However, you are less efficient in exposing those ores (11 ores exposed per 3 blocks mined versus 8/2 with branch mining or using the method above). Vertical travel times/trip approximately halved. The largest advantage is being able to safely jump down nearly instantly. I wasn't able to find the travel speed on a ladder, though I believe it's slightly faster than walking. In addition, you can eat while climbing ladders without being slowed down, which is not the case with stairs. Less space required.Mobs could potentially exist in the middle of a step tunnel.Every miner has their preference, and these difference amount to mere seconds/trip. I merely recommend trying different methods to determine which you prefer. Important Safety Considerations When Mining:Never dig straight down. You could fall straight into lava, a ravine, a creeper, etc...Never dig straight up. If there's an ore above you, step back, have a block ready in case lava is exactly above, and be ready to back up quickly if a creeper drops down.Explore and light caves before mining ores. A dark cave can spawn mobs, which you may approach you from behind while you're mining.Use water to obsidify lava. Unless you're really low on torches, there's no reason to leave lava as lava. It's just an extra hazard.