Your breath is a wonderful tool you can use to center yourself.  Experiment and breathe in to the count of six, and breathe out to the count of three.  Stop reading and breathe like this for one minute. . . 
 

Notice what you are feeling.  What is different?  Look around the area that you are in.  How have the colors changed?  What is going on in your body?  Do you feel a little light-headed?  How long does the light-headed feeling last?  Are you aware of any new aches or pains in your body?  Did any aches or pains disappear?  What are your thoughts?  Are there more thoughts or less?  Okay.  Do it again.  Breathe in to the count of six and out to the count of three for another minute. . .
 

Notice what you are feeling.  You are more centered now then you were two minutes ago.  Nice.
 

Besides centering and quieting yourself you can also build your self-esteem by breathing.  As you are breathing as indicated above, visualize someone you love and respect in a chair facing you.  See the two of you breathing together in a gentle, loving rhythm.  Now, visualize yourself setting in a chair facing you and give yourself the same love and respect.  Do this for a minute. If you find yourself drifting off, don’t be concerned.  Just refocus and breathe in to the count of six and out to the count of three. . .  Enjoy breathing you.