Place lower calves against the padding and have hips on the edge.
Swing upwards until your legs are roughly parallel to the ground.
Swing back down to the start position and repeat.
Hyperextending at the top.
Losing contact with the leg padding.
Upper body swaying too much.
Adjust so you can place your lower calves against the padding and position yourself face down with your hips resting just off the padded platform. Grip the handles at the front.
Start by slowly lifting your legs up to begin swaying the weight to build momentum until your body makes a straight line. Drive your legs backwards on the way up but then drop them down with the weights on the way down. Keep your legs straight throughout the movement. Repeat for the desired repetitions then lower the rep ranges until the weight is still.
Always perform the movement in a controlled manner, avoid rushing repetitions.