Drill starts off with a line at center court.  The 1st two players in line have a basketball.

There are two players at top of the key (Player 1 & 2).  And there's one player at the bottom corner of the court (Player 3).

Player 4 passes to Player 1 at the key and then breaks for a lay-up.

Player 1 passes the ball to Player 4 and follows behind Player 4 as he makes his lay-up.  

Player 2 moves over and takes on the position Player 1 had.

Player 1 gets rebound and outlet's ball to Player 3.  

Player 4 moves to the top of the key taking the position held by Player 2.

Play continues at half court with Player 5 passing to Player 2.

Player 3 passes the ball to Player 6 at half court.  Player 3 then follows his pass and moves to the end of the line. Player 1 moves over and takes position of Player 3.
Player 2 passes the ball to Player 5 and follows for the rebound.  Player 4 moves over and takes position held by Player 2

The drill continues in this fashion.

I emphasize:
Good leading passes to the basket.
The passer not letting the ball hit the floor as he rebounds the lay-up.

I use two balls for the drill so that the motion is continuous.