Another method of centering yourself is to play a simple game called "Now I Am Aware." Going slowly, simply focus your awareness on one aspect after another of your here and now experience. Take the time to really notice whatever you bring into your field of awareness, be it a sound, a sight, a smell, something you touch, or something you taste. Go slowly. As you gain relaxed control of your spotlight of awareness, experiment with relocating it from your body - to the world around you - to the world of mind, staying a few seconds in each place. As thoughts come into your awareness, simply notice them and let them go. Gently direct your awareness back inside the boundary defined by your skin, or outside of it, beginning phrases with "Now I am aware of..."
As for me:
"Now I am aware of the sound of the pencil lead on the paper;
Now I hear music in the background;
Now I am aware of the breeze on my skin;
Now I am aware of thinking about what to write;
Now I am aware of a tightness around my eyes."
It strikes me that this is a good exercise to practice when we're out and about our daily business. You can do this any time - standing in line at the bank, waiting for the red light to change, taking a break between tasks. It's really very illuminating because it gives us information about how we're so often not aware. Try it and see how your overall mindfulness improves.