Hold the ball up under pressure and link the play. Get side-on with your back to the defender, keep the ball on the far side, feel the defender with your arm, and lay it off to support at the right moment.
A server plays into a target with a defender pressing from behind and a supporting player deep. The target shields the ball, protects it as the defender tries either side, and lays it off to the runner, who recycles it. Keep the body between the ball and the defender at all times. Progress to holding up and turning to shoot.
Shielding is legal obstruction, and the laws allow it under one condition: the ball has to remain within playing distance. A player who keeps it there can put his body wherever he likes between the opponent and the ball, and the opponent has no lawful way through. Let it drift a yard further and the same body position becomes impeding, which is a free kick against.
That rule is the whole technique, and stating it changes how players practise. The instinct when a defender leans in is to push the ball away from him for safety, which is precisely the movement that turns a legal shield into a foul. The correct response is the opposite: keep it closer, usually on the foot furthest from the defender, and accept that safety comes from body position rather than from distance.
The arm is where players get penalised without understanding why. An arm held across a defender to feel where he is, bent and passive, is accepted everywhere. An arm that extends to push him away is a foul in any competition, and the difference is visible to a referee from thirty yards.
Stay low and wide. A tall, narrow player is easy to move off the ball, and getting the centre of gravity down does more for holding possession than upper-body strength does, which is worth telling smaller players explicitly.
The honest limitation is that shielding creates nothing. It buys two or three seconds for support to arrive, and a player who shields brilliantly with nobody running past him has achieved a stationary ball in a crowded area. Coach the arrival at the same time.
Save it to your private drills, then change the animation, adjust positions, swap equipment, or drop it into a session block. Or start from a blank pitch and build your own.