Position your feet evenly on the platforms and position yourself against the padding.
Drive one leg straight back, then bring it forward.
Drive the opposite leg back as the other leg is coming forward and repeat.
Rushing repetitions.
Lacking control.
Moving the upper body too much.
Adjust the padding to allow your feet to be roughly in the middle of the platforms when your shoulders are against the padding.
Start by driving one leg backward as far as comfortable, as one leg comes forward start driving the opposite leg backwards. Tense your core to keep a straight back throughout. Repeat for the desired amount of repetitions.
Avoid rushing repetitions or limiting your range of motion.
Fitness for all, for life.