Smart Way:

1.Have 4-7 Iron Pickaxes.
2.Make a stair mine about 5 stairs,go straight about 10 blocks forward,and repeat!
3.Hit bedrock
4.Jump-place-block about 3 blocks,then keep going straight 3x3 or 2x2
5.Find Diamonds
6.Be sure there's no lava under diamonds.
7.Found only 1 diamond? :'[ then dig around.

Stupid Way:

1.Have precious items.
2.Dig straight down.
3.have no food.
4.be on easy,normal,hard.
5.find diamonds.
6.keep digging.
7.10 seconds later,you find lava.
8.and you fall in and die. :'D