This is a deep dark secret for which the answer is not readily available. Criterial for all academies are basically the same. You should be able to search this site and find both maximums and averages. You WILL NOT find the minimums. The reason for this is that the academies want you to do your best. Do that.
Practice, practice, practice. Experiment, experiment, experiment. Technique, technique, technique. If your hands are large enough, try getting the ball up on your fingertips for extra leverage. Your knees must be perpendicualr to the line of flight but your upper torso does not. Use the advantage gained by rotating your torso from one extreme to the other. Then practice some more.