After you find a comfortable position on the floor, stick your legs as straight up in the air as you can. Knees should be slightly flexed. Flex your ankles by bringing the toes towards your face. Breathe into your legs. Some vibration should occur. You can also put your hands around your lower legs and pull the legs toward your head, slightly, hold and then release. Allow your legs to vibrate for a couple minutes and then put them down.
Picture is from The Way to Vibrant Healthy: A Manual of Bioenergetic Exercises, by Alexander Lowen, M.D., and Leslie Lowen, p. 30.