This is the second way of mining, and it actually involves very little mining. Most of the time is spent finding and exploring different caves, tunnels, and prebuilt mines. What you need to do is go out and search for entrances for different caves. These are usually found around mountains and hills. Some caves you can see from far away. They will be much darker than everything else around, almost black. If you dig down far enough, you will most likely find a cave or two. The caves underground can be very big, but be careful, monsters can survive, even in the daytime, in dark areas.
Once you have found a worthy cave you’ll need to grab some torches and go exploring, just keep planting torches and search around. One tip is to put torches that lead you back out of the cave on the walls, and exploring torches on the floor. This way you can easily, and quickly, get out of the cave if needed. You should find plenty of iron and gold in a cave that is pretty big, but underground caves seem to have more diamonds. In fact sometimes caves can be filled with dozens and dozens of minerals. You can do this for every single cave you find and you’ll be rolling in minerals.
Out of these two mining techniques the first one is much more reliable but it takes much more time and sometimes it can be a little boring. The cave exploring technique is much more exciting but it can be hard to find a good cave to explore properly. Of course there is the added danger of finding a cave filled with creepers and other dangerous mobs. It is usually best to use a mix of both mining techniques.