A recipe for bhramari breathing
It's better with shan-mukhī mudrā six-mouth seal. I won't decribe that here but the key element is the blocking of the earholes with the thumbs.
Bhramarī is a mode of pranayama, but probably also regarded as a mudrā (literally, sealing/sign), since the name is a feminine adjective (‘bumblebee-like’): pranayama is a masculine noun and mudra a feminine one.
The short form of this recipe is just ‘pay unhurried attention to your inhalations’ during bhramari, but here’s the long form:
stop breathing in.
Start humming, shape the hum:
Have the lips vibrate; the teeth might be slightly apart. You can experiment: seek forms of resonance that suit you. Up into the cranium? Back into the throat? Shape the mouth space by raising or lowering tongue, and manage the form/width of the cheeks. You can vary the sound from breath to breath, especially at first. Accidental throat singing is ok.
Constant hum, control the abdomen:
Then keep the sound constant for rest of each hum. Manage the evenness by observing the motion in the abdomen, but keep hands, face, shoulders relaxed.
Stop humming and finish exhaling:
Instead of ending the hum and the exhalation at the same time, stop the hum in good time before the breath has been completely released — don’t strive to protract the duration. Finish the exhalation without changing the form of the mouth. The only thing that changes is that you stop making noise. Don’t mark the break in the shift to the next inhalation.
Relish the inhalation: the breath returns into the space of the hum: you might think of your mouth as a cave by the sea. Holding the silent mouth in the form of the hum can be taxing; if so, let the mouth soften at some point during the inhalation.
The main aim of this recipe is forestall the natural tendency to treat the inhalation as just fuel for the real business of the humming (as when we breathe to talk, sing, whistle etc). Humming with the ears sealed takes us into the spaces of the cranium: inhabit those spaces as you inhale as well, and inhabit the contrast of silence. The entire mode can be thought of as alternations of sound and the relative silence. The humming side of the breath requires focus and is a form of work; and the sound filling the head blanks out other kinds of sensation. Both of these drop away during the inhalations: we want to feel we are in a kind of quiet aftermath.
A nice practice is to do a run of continuous bhramarī breaths (5 or 10 or whatever suits, but enough to get it well established), then begin inserting non-humming breaths while still holding on to the aftermath. Gradually increase the gaps until you decide it has finished.