Diaphragmatic or deep breathing is probably the most widely used reactive stress management technique.  Give it a try the next time you feel under pressure or are stuck in a tense situation.  Maybe you have an irate customer on the phone who is being unreasonable and aggressive.  You can feel yourself beginning to get angry and losing control.  Try the following while listening: take several slow, deep breaths into the pit of your stomach, follow this with some normal breathing, then take several more deep breaths.  Most people are surprised at how well this simple exercise calms them down and clarifies their thinking.