React quickest to the second ball. Read the aerial duel, anticipate where the knockdown drops, win the loose ball before the opponent, and break forward off it.
A long ball is launched into a contested area. Players duel in the air, one heads a knockdown, and both teams react to win the loose second ball, with the winner breaking forward. Emphasise reading the flight and the duel, gambling early on where it drops, arriving first, and breaking at speed off the regain. Vary the launch and the duel. Rotate the roles.
Long balls are decided twice. The first contest happens in the air and gets all the attention, and the second happens on the floor a second later and decides who actually has possession. Teams that win headers and lose matches are usually losing the second contest, and it is far more coachable than the first because it rewards reading rather than height.
Anticipation is the whole skill. A knockdown does not land randomly: it goes roughly where the winning header sends it, which is usually backwards from the direction of the ball or sideways off a defensive header. A player who watches the duel and then reacts is always second. A player who reads the duel while the ball is still in flight, judges who is favourite and moves to where that player's header will drop, arrives first.
The positioning cue worth teaching is to be behind and around rather than underneath. Standing directly beneath two players contesting a header means the ball goes over you as often as to you. Positioned a few yards behind the duel on the likely side, a player covers the majority of outcomes.
Gambling is part of it and should be permitted. A player who commits early to where he thinks the ball will drop will sometimes be wrong and look foolish, and will win considerably more second balls than one who waits to be certain. Coaches who criticise the wrong guesses will train that instinct out.
The break afterwards is what makes it valuable, because a second ball is won facing forwards against a team that has committed bodies to the first one.
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.