Below is a session I created for my U14 FC Boston Bolts team. The main focus is on understanding and executing the fundamental principles of defending in small numbers. Important things to emphasize are :
1.) pressure... closest defender to the ball is the immediate pressure on the ball. Close space down quickly, but slow your speed down once approaching the ball so that you dont overcommit. Show attacker one way by curving your run and using correct body positioning. Squeeze on poor first touch or if attacker's head goes straight down.
2.) cover.... defender should be off the pressuring players shoulder (45 degree angle). If pressure is beat, they are able to step and become pressure. Find balance between not being too close to pressure (so 1 pass doesnt beat both of you) and not too far away (so that you can still cover the pressure player if he is beaten on the dribbler).
3.) balance.... eyes for the pressure and cover. Balances out the field, further away from the pressure. Because balance is the eyes, they need to communicate! Player needs to be able to open hips and see both the wide attacking player and where the ball is. If pressure player is beaten, cover steps to be pressure and balance also tucks in to be cover now.