You will spawn in a little forest in a mesa biome which is really big. At spawn start digging straight down.
It will take quite some time but eventually you will get to get the cave and tunnel system with lots of ores to be mined.
Once you get into the tunnel system the floor will be flooded with water. Locate where the water is coming from and plug the hole with a stone block.
As soon the water is gone you will be able to see the 10+ chunks of coal. A little bit to the left is also one lonely diamond block.
There are multiple tunnels leading different ways. It doesn’t really matter in which direction you go first because either way you will stumble upon multiple chunks of iron, coal and even some diamonds without having to dig.