Train the very short combination that beats a tight defender, and link it to what happens next. Players learn to play a one-two at close quarters, then release past a second line and carry the ball into a shooting position.
Set one mannequin as the first defender and three more as a second line nearer the goal, with a full goal and keeper. The player on the ball plays a short one-two around the first mannequin, receives it moving forward, then releases a pass of about ten metres past the second line. The receiver carries the ball eight or nine metres and finishes. Keep the first exchange genuinely tight, within two or three metres. Run several balls and rotate through every role.
Most one-two practices are played at ten metres, which is comfortable and largely misses the point. A wall pass at ten metres is just two passes. The version that actually beats somebody is played at two or three, right on top of the defender, in the space where he can nearly reach it and where a heavy touch is fatal.
This drill puts the first exchange there deliberately. The lone mannequin is the first defender, and the combination happens close enough to it that the pass and the return both have to be precise. Widen that exchange and the drill still runs, but it has stopped training the thing that is hard.
What makes it more than a technical exercise is what comes after. Beating the first man is only useful if you can then do something, and the sequence immediately demands a ten metre release past a second line, followed by a carry and a finish. Players quickly discover that a scruffy one-two, even a successful one, leaves them off balance and facing the wrong way for the pass that follows. The quality of the first exchange shows up two seconds later, which is exactly how it works in a match.
The common failure is timing rather than technique. Players get through the first mannequin, then hold the ball while they look up, and by the time they release it the second line is on them and the pass has to go backwards. The release should be made early, while there is still space to play into, which means deciding where it goes before the return even arrives.
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.