I have begun to practice a daily warm up which goes as follows:
1- Sigh into the instrument with a soft embouchure, increasing the sigh speed and embouchure until an airy tone comes out. I start on a low C and go up the scale sighing out each note with lots of air, taking notice not to overtense any muscles. Each note speaks only for a few seconds before I run out of air. The purpose of this exercise is to engage deep and fast air to create and control tone.
2- Take a big breath, more like a yawn, and hold the air full, as if breathing in a bit more. I do not close the throat, as this defeats the purpose of exercising the "inhale" muscles. From this "lifted" position, I huff a note with an air attack. After each huff, I lift/inhale again. So each note only expels a bit of air, and the rib cage stays up and open. I use perhaps 3% of my air for each soft huff and immediately inhale/lift again. I do this up and down a scale, such as C. The purpose of this exercise is to a) learn about the inhale muscles in the upper torso and b) to learn how to exhale without collapsing the ribs and back down, a common problem for many players.
3- Turn on the evil decible meter (from Radio Shack), which I have named Jezebel, and proceed to (attempt to) play long tones, a) all pp b) with crescendo and diminuendo. The purpose of this is obvious- to learn about and gain absolute control over tone production and volume.
Though I have barely made a sound, this process fine tunes my support and tone control muscles to a great degree. It takes me at least a half hour to explore deeply and can gobble up more time. Today I did it for an hour.