I'm not a big fan of breathing exercises. Breathing, I like. Exercises, not so much.
I'm not sure why. Maybe it's because time is always limited. Maybe because I'm not patient enough. The buzzing exercises I start with usually require some pretty deep breathing so maybe my cause isn't totally hopeless.
Last Fall, I tried this little exercise in a few lessons and, from time to time, I've used it in my practicing.
Take three really deep breaths and, each time, blow out like crazy.
I blow out mostly (but not completely) through my horn. I let some air escape around the sides of the mouthpiece.
I think of this quick exercise as a "lethargy buster." When I (or my students) get a little sluggish, this is a quick way to wake up and get going.
I remember trying it in three lessons in a row last Fall. Not at the beginning but somewhere in the middle when my "sluggish radar" began beeping. Each time, I was surprised and please with the improvement in their sound.
(I did warn them not emulate that wild, almost psycho manner of blowing out when they actually played.)
This is not my invention. From the Alessi Seminar, I remember Weston Sprott doing similar crazy breaths from time to time. In fact, checking a handout on his website, I see that he refers to it as the "vigorous breath."
Somehow, "big bad wolf" just seems more memorable...