This is an excerpt from Weight Training-5th Edition by Thomas R. Baechle & Roger W. Earle.
The *landmine shoulder press is designed to develop the shoulder muscles but will also develop the deltoids and triceps muscles. Because of the balance required to perform this exercise, it is more appropriate for experienced lifters. This exercise can be performed with a barbell while standing or kneeling and in a split or normal shoulder-width stance. It appears, however, that the best stance for isolating the shoulder muscles is the kneeling split stance, which is shown in figure 6.5.
Establish a split-stance kneeling position, with the back knee on a cushion and the forward knee flexed at 90 degrees with the forward foot firmly in contact with the floor. From this kneeling position, with one end of the barbell anchored to the floor and the free end of the barbell held with a pronated grip, lift the barbell to shoulder height. To start the exercise, position the barbell directly in front of the forearm, then lean forward and press the barbell to overhead position until the elbow is fully extended. At this point in the exercise, the back knee, the hip and shoulder on that side of the body, the head, and the overhead hand with the barbell should form a straight line. Exhale during the overhead pressing movement. To return to the starting position, allow the elbow to slowly flex until the hand reaches shoulder level. Inhale during the downward movement. After completing a set, reverse the knee stance positions and complete upward and downward movements with the opposite arm.