1. You'll need a Dog. A dog with a big mouth is even better.
3. A long durable hose.
3. Lots and lots and lots of water.
4. Did I mention a freakish dog that loves the hose?
NOTE: Do not use traditional sprinklers to achieve your green lawn. The freakish dog will eventually get brave enough to bite the sprinkler, lift it from the ground, and destroy it, causing a slow painful death for the sprinkler, bringing you back to hand watering the lawn with the dog, see #1.