Start by adjusting the seats depth to allow your knees to bend over the bench when your back is firmly against the seat. Adjust the bottom pads angle so that when you're seated your ankles are just in front of your knees, then adjust the pad's depth so its against the front of your lower shins.
Begin the exercise by extending your legs upwards to a point where they are almost straightened but don't lock them out. Then in a controlled manner lower them back down to just before the starting point to avoid clashing the weights. Concentrate on using your quads to move the weight rather than pushing your feet up and remember to keep your feet straight. Use the handles on the sides to stabilise yourself when performing the movement. Repeat for the desired amount of repetitions and then gently rest the weights back down.
Control the weight throughout the entire movement where you avoid kicking your legs up for momentum and free falling the weights on the way back down.