All brass playing starts with two physical variables: air and embouchure, and students must have basic understanding and control of both before adding instruments to the equation. Air is the generator on which brass music runs. Air generates vibrations that, when funneled through a mouthpiece and amplified by an instrument, project as characteristic and beautiful brass sounds. If you are reading this, you have used air all of your lives. You know how to breathe naturally, and you should take a natural approach to breathing to play brass instruments. Contortions, tension, and unnatural manipulations of the body to produce air for playing are ultimately counterproductive. Breathing must be quiet, relaxed, and efficient for successful performance.
Embouchure refers to the positioning of the lips, jaw, teeth, tongue, and all of the other facial muscles that engage in wind instrument playing. In brass playing, the lips offer resistance to air passing through them, which translates into vibration or buzzing. These vibrations are what the instrument amplifies into projected sound. Learning to manipulate these embouchure muscles in relation to the air stream is the primary physical basis of all sound created on brass instruments.
Once students can audiate what they will play, they are ready to start to learn the physical aspects of their instruments. Again, teachers must temper the excitement and anticipation of making noise on instruments with good pedagogical sequences and thought to what will set students up for success. All teachers will tailor instruction to their own situations, but merely assembling instruments and letting students go at it without specific guidance will lead to the formation of bad habits and disorganization in the classroom more often than not.