During ground school I was taught a variety of important maneuvers as well as hand signals that are given by fellow skydivers to insure safety.
After jumping out the plane (sounds scary right?) the skydiver should immediately arch their back and position their arms so that they make a “box” as pictured. The hand signal that accompanies this movement is a “thumbs down” to signify pushing the hips forward. My arms are not in the right position in this picture -- they should be closer to my head.