You will want to prepare yourself ahead of time with several stacks of planks, several stacks of torches, plenty of coal, MANY stone pickaxes, a couple steel pickaxes, a bow with several stacks of arrows and a good sword. You might not have all of this if you’re in a new world, but get as much of it as you can beforehand.
Step 1: Never Dig Straight Up or Down
Never dig straight up or down, you run the risk of getting killed by a hazard or enemy.
Step 2: Always Place Torches As You Go
Always place torches as you go, but more importantly, as your cave gets larger, always make sure you make the exit EXTREMELY visible so you can find your way out.
Step 3: Kill Everything You Run Into As Soon As You Can.
Kill everything you run into as soon as you can.
Step 4: If You Dig Against Something Above Floor Level and You See Lava
If you dig against something above floor level and you see lava, block it off immediately or it will spread to you.
Readmore: The 3 Steps to Mining Effectively in Minecraft
To begin, you will want to find a place close to the area you call “home” and store your stuff. Make sure it’s easily accessible, because it doesn’t really matter where you start. When you begin digging down, make sure you’re doing it in a staircase fashion so you can easily exist. Your goal is to find a giant underground cavern to explore. Once you have your underground cavern you will want to begin exploring, but make the place easy to explore as you go. Reform it so you can easily get from place to play without much trouble. This, as well as torches, will allow you to easily find your way out.
Remember, when you find gold, diamonds and red stone, you must use your steel pickaxe. For obsidian you will need a diamond pickaxe. For everything else your stone pickaxe will do, including steel. If you want to find diamonds, you can press F3 to see your depth (it’s the Y variable). You will want to be at around 5~10 and dig in a straight line. Once you have your diamonds and your diamond pickaxe you can mine Obsidian, which is made by dumping water on lava. You’ll either need to reroute some underwater streams into lava or use a bucket.