Score from a near-post flick-on. Attack the near post early, glance the driven ball on across goal with a flicked header, and arrive at the back post to head the second ball in.
A server drives a flat ball to the near post. The first runner attacks it early and glances it on with the side of the head, and a second runner arrives at the back post to head it in. Emphasise attacking the near post ahead of the marker, using the pace on the ball with a small flick, and timing the back-post run late. Practise both the flick and the finish. Rotate the roles. Heading loads: no deliberate heading at U11 and under, and at U12-U13 keep it to roughly 15-20 headers in a session and under 30 minutes of heading a week, using a correctly sized and properly inflated ball (US Soccer and FA guidance).
Defences organise against the ball's current direction. A flick-on changes that direction by a few degrees at the near post, and everything set up to deal with the original delivery is suddenly facing the wrong way. That is the whole mechanism, and it explains why a flick needs contact rather than power.
The pace is already on the ball. A driven near-post delivery arriving at speed only has to be touched to keep travelling, which is why the instruction is to glance it rather than head it. Players who try to generate their own power on a flick almost always mistime it, because a full heading action needs the ball to be in a specific spot and a fast delivery will not wait.
Contact is with the side or top of the head rather than the flat forehead, which is the opposite of what every other heading drill teaches. That is worth saying explicitly, because a player told repeatedly to use his forehead will square up to a ball he should be glancing and stop it dead.
Winning the near post is what buys the chance to touch it at all. Attacking in front of the marker, early and hard, means arriving before the defender can get his body across. A flick-on attempted from behind a defender is a header the defender wins.
The runner behind is the point of the whole thing. A perfect flick into an empty back post achieves nothing, and the arrival should be timed to the delivery rather than to the flick.
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.