Another brain gym exercise from Paul and Gail Dennison's book, Brain Gym is called belly breathing.  I use it whenever I'm feeling tense or nervous.  Standing up, I rest my hand on my abdomen and thenblow out all the old air in short, soft little puffs (like blowing a cotton ball).  Then, I breathe in slowly, with a dep breath, filling up my abdomen like a balloon.  I do this for about 4-5 times and always feel more relaxed and calmer.