I always start a phrase with a full breath. Some schools of playing only inhale as much as they are going to expel, but I enjoy the feeling of starting a trip with a full tank.

Almost all brass players talk about breathing (we do play WIND instruments, after all), so there must be something to it. I try to keep the subject as natural as - well, breathing. Sometimes you can listen to brass players talk about breathing at great lengths, and not hear them mention the LUNGS even once! Yet, you can ask almost any 9-year-old about breathing, and the answer will most certainly be about the lungs. Its curious that we tend to lose sight of the simplest, most natural things, sometimes. Chest breath, stomach breath, high breath, low breath: I believe that if your posture is good, and your breathing is unobstructed and natural, then you will be breathing properly.

Breathing between phrases is an important issue. Our goal should be to inhale as fully during the instant between the phrases as we did before the piece began. To do this we must:

Play the preceding phrase to a nice conclusion, including the end of the last note.  (The shaping of the phrase and final note are key in setting up a good breath.)

Take the mouthpiece off the lips.
Open the mouth.
Inhale quietly and fully.

Sounds simple, is simple. It may at first take more than the instant at our disposal, but with many perfectly executed repetitions it will become quick and natural. It may be necessary to exaggerate the procedure at first in order to root out bad habits. I liken this to a baseball pitcher's windup. When no one is on base, they take a protracted windup, but as soon as a runner is on they cannot take so much time (the runner would steal the next base!), and so must "pitch from the stretch". Despite the shorter windup, they must still get the same velocity. Between phrases, then, we are "pitching from the stretch".

One further thought about breathing: We learn in Physics 101 that "nature will not tolerate a vacuum". A vacuum is an unnatural state in our world. Now, if you expell your air to the end, while maintaing good, upright posture, you have a degree of vacuum in your chest cavity. Normally - by physical law - you must only let it, and nature will fill it again for you! Try it. Let it work for you. When a baby is born, the doctor - usually through a well-placed swat - helps the baby vacate the lungs of the fluids that have filled them in the womb. He does not then have to explain to the baby how to take in the air. It just happens! Let's not turn one of life's most absolutely natural and simple functions into a rocket science!