This is the beginning exercise in teaching and learning jumps.
Take an upright stance with knees slightly bent, chest out, and shoulders back. 
Begin by emphasizing a vertical takeoff, projecting the hips upward for height, using only the lower portion of the legs. Use the arms and shoulders in an upward blocking fashion. Emphasize slight flexion and extension of the knee, and more flexion of the ankle and foot.
Upon takeoff, the ankle must lock the foot into toes-up position, maintaining this locked position throughout to ensure sturdy contacts and quick, elastic takeoffs.