Sitting or lying down in a comfortable position (savasana is the "corpse pose"), take a minute or two to breath deeply and relax. Close your eyes and bring your focus to this present moment and your physical self. This is a physically passive technique, so you do not need to move, flex, or do anything else with your body. Having said this, there is nothing wrong with taking some physical action if you feel that it would be helpful. Begin the body scan by drawing your attention to any particular part of your body. Try starting with your feet. Tune in to what is happening in your feet. What do you notice? Do your best to remain as passive and non-judgmental as possible. (Remember, you are an objective observer of your own subjective experience.) At the same time, carefully observe your feet, both deep inside them and on a surface level. If you notice tension, tightness or contracted muscles, consciously release and relax those areas.
As you feel ready, progress up to your lower legs. Again, notice what is happening in your lower legs. Carefully observe your lower legs, both deep inside them and on the surface. Again, if you notice tension, tightness or contracted muscles, consciously release and relax those areas. Progress now to the upper half of your legs and notice them. From there, move on to your buttocks, waist, and lower abdomen. Next, focus on your middle abdomen, sides, and back. Your chest and upper back are next, followed by your shoulders, upper and lower arms, and then hands. Once you have finished focusing on your hands and fingers, move your attention back to your neck. Finally, turn your focus to your face, jaw, eyes, ears, and skull. Finish this exercise by taking a few more deep breaths and turning your awareness back to your entire physical self, which includes all of the parts on which you have been focusing.
For a quick body scan, try focusing on larger sections of your body (for example, notice your legs as one section). For a more in depth body scan, try focusing on smaller sections of your body (for example, each finger or even each toe). A quick body scan can take 30 seconds. A longer body scan can take 30 minutes, or more. Based on your needs and circumstances, this exercise can be very flexible.