Learn how to regulate your sympathetic nervous system with diaphragmatic breathing. I know that meditation has been mentioned various times, but breathing as a subset of meditation is useful whilst sat in a meeting or conference, as it's approaching your turn to speak. It has worked wonders for my state of mind before public speaking.
One can vary the pattern to determine what works best for them. For me it's "in for 5, hold for 5, out for 5". As in breathe in slowly over five seconds, hold for five seconds and than exhale over five seconds.
