1.How to find ORES such as diamond,lapiz lazuli , redstone,coal and iron or maybe gold.
Dig down to the bottom of minecraft.
Make stairs going up 10 steps.then dig to the left and right
this might not work but you could find a dungeon.

2.If you find redstone,diamond or any ores except from coal and iron,do not dig it out unless you have an iron pickaxe or better.otherwise they will dissapear.

Zombies,Creepers,Spiders and skeleton archers spawn anywhere in the dark as long as its not on peaceful.So when your digging make sure you put a candle down to light the room up.