Sit in your chair, upright but comfortable, with your back supported. Let your body relax (without slouching), with your feet on the floor in front of you and your hands at rest on your thighs or joined in your lap.
Close your eyes, or fix them on some point in front of you. Now let your whole attention focus on what you can feel in your body. You may start at your feet and work upwards, letting your attention dwell, perhaps only for a few seconds, on whatever part of the body you can feel, shifting attention from one part of the body to the other, although the longer you can hold attention on one part, the better. Your attention is on what you are feeling, not on thoughts about feeling. If you are uncomfortable, or itch or want to move position, just acknowledge the discomfort, assure yourself that it is all right and, without moving, continue to focus attention on what you can feel in the body.
The mind rarely leaves us long in peace to do this, but begins to demand attention with comment and questions: This is a waste of valuable time. What has this to do with prayer? Is this some kind of Hindu thing? What is the point of it? Deal with the questions and comment as you dealt with the itch; acknowledge them, then return to feeling the body.
You can, if you like, move into more explicit prayer by repeating to yourself St Paul's phrase, In him I live, and move, and have my being.
(adapted from God of Surprises by Gerry W Hughes SJ)