Practicing finishing on corner kicks.  Have someone taking corners from each side. Three cones at the top of the box.  The line closest to the corner where the ball is kicked from runs near post, middle cone goes to the PK spot and furthest cone makes a curved run to the back post. Once the ball is kicked everyone attacks the ball quickly.  Alternate the side the corner comes from and keep everyone in the same line.  Once everyone has gone through 3-4 times, rotate each line to a new cone.  Alternate the person taking the corner kick. 

2 points of focus - (1) Those attacking the ball with speed and urgency. (2) Proper form for those taking the corner.  Wider step for plant foot and following all the way through the ball, finishing with leg in the air.