Some problems with tone, embouchure, breath support, intonation can all be caused by not breathing properly. First of all, put your hand over your stomach, take deep breath’s pushing your stomach in and out and not letting your chest and shoulders rise. All your breathing should be controlled through your diaphragm and no upper body movement should be made. Concentrate breathing completely from your diaphram. When you breath from your chest, your sound will be smaller, less focused and thinner sounding. Intonation will be more of a problem with added response problems. Furthermore, when you get nervous your chest tenses up, air becomes trapped in the lungs and you find yourself taking breath’s every measure. Breathing from your diaphragm will actually help relax you. Your air stream will become more focused, fuller sound, better intonation and your embouchure will be more relaxed because you’re using good air support.