Set up on the leg press is with the seat lowered so the hips are in line with or just below the knees. 

To adjust the seat, pull up on the yellow handle and lower. 

Place your feet hip to shoulder width apart and in the center of the foot pad. This will ensure you're working the quads and the glutes. 

With your chest tall and belly tight, drive your feet through the pad until legs are fully extended, then lower slowly back to the start.