Player 1 carries the puck down a wing (most times they will be pushed outside by the defense).
Player 2 should go to the net.
Player 3 should be in the high slot.
This helps the players learn to go to the right spot and not stand and watch the others with the puck.
Variations would be to have players (or coaches) play defense to make them move the puck or go to different positions.
If you are looking for additional help with positioning, check out:
4 on 2 forecheck
4 on 2 puck movement