At spawn there are one large pig (a sow) and two cute piglets walking around. So incase you get hungry there are three meaty beefs waiting there right at you. Anyways, if you dig straight down at spawn you should soon reach a pretty big cave and tunnel system.
Once in the tunnel system there will be two ways of choosing from. Choose the one which there is a mineshaft closest to.
The mineshaft itself is really big but be on a special lookout for where there is a fire and lava, it should be in one of the mineshaft tunnels. Put out the fire and lava to see the first diamond.
Once you start mining the first diamond ore and the stone blocks surrounding it you will find a total of two more diamonds at the same location.
The cave is literally stuffed with diamonds but there are still some exploring and searching you will have to do to your own to find them. Though, most of them are openly available and don’t require any mining to find.
Seed: still notch