I do this with the bar to help me with learning to pull under the bar better. I do a 3 position pull under with the bar. Then i do the same thing again with 40 kg's.
It would go like this 1-2-3 then take a short break and do it again. I do it about 3 times with just the bar then 1-2 times with 40 KG.
All snatch grip, focusing on getting "tall", fully extended, or what ever you coach might call it, then pulling with the arms at the very end.
Knees slightly bent then Explode Under The Bar (EUTB) with basically just shrug and arms. This has really helped me with pulling under especially when i put some weight on it.
Knees and back bent bar at mid thigh then EUTB.
Bar at knees then EUTB.
Two things are really important.
First is do this fast, speed is the name of the game.
THE SECOND AND MOST IMPORTANT IS TREAT EVERY REP LIKE IT IS AN OPENING ATTEMPT. DON'T CRUISE THROUGH YOUR WARMUPS THIS IS WHEN YOU ARE ESTABLISHING YOUR MOTOR PATTERNS. IF YOU ARE LAZY AND SLOPPY HERE YOU WILL BE EVEN MORE SLOPPY WHEN THE WEIGHTS GO UP.