Bring your attention to the tip of the index finger of the left hand. The next time you take your normal breath, simply let you attention run slowly from the tip to the base of the finger. As you exhale normally through the nose let the energy stay in the finger and return your attention to the tip of the finger. Repeat the procedure again with the next breath.
As a sensation of heaviness or warmth develops in the left index finger compare it with the right index finger, where you have not done any bone breathing. This will help develop your ability to feel more deeply and identify the sensation bone breathing brings.
As the left index finger becomes warmer or heavier continue the same bone breathing procedure with the rest of the fingers of the left hand, either one by one or all at the same time. As the left hand becomes warmer and heavier compare it with the right hand.
When you decide to incorporate the right hand into the practice simply reproduce the feeling of the left hand in the right, or start once again finger by finger. Once both hands are feeling heavy continue the same practice but higher and higher in the arms until the same feeling is up to the shoulders.
For bone breathing through the feet it is best to remove the shoes and any tight clothing and guide your awareness up the toes, either singly or together up to the ankle.
For breathing up the spine begin at the tip of the sacrum and run your awareness up the spine higher and higher until you reach the base of the neck and the same feeling of warmth and heaviness is developed.
As the practice progresses and the body relaxes, the gross breath through the nose may become more and more subtle. Do not try to force it back to gross, but rather, let it stay subtle and calm. Continue to guide your attention up the bones. Eventually it is possible to have the whole skeleton, including the teeth, doing bone breathing.
As practice develops try to breathe through the whole body at once, like a sponge.
If more specific knowledge of the bones is desired then try to work with an anatomical chart of the skeleton to guide the energy with more precision.