In this interesting article, Pema Chodron gives concise and practical advice on the practice of Tonglen. She mentions:
Tonglen practice, also known as “taking and sending,” reverses our usual logic of avoiding suffering and seeking pleasure. In tonglen practice, we visualize taking in the pain of others with every in-breath and sending out whatever will benefit them on the out-breath. In the process, we become liberated from age- old patterns of selfishness. We begin to feel love for both ourselves and others; we begin to take care of ourselves and others.
Tonglen awakens our compassion and introduces us to a far bigger view of reality. It introduces us to the unlimited spaciousness of shunyata (emptiness). By doing the practice, we begin to connect with the open dimension of our being.
Tonglen can be done for those who are ill, those who are dying or have died, or those who are in pain of any kind. It can be done as a formal meditation practice or right on the spot at any time. If we are out walking and we see someone in pain, we can breathe in that person’s pain and send out relief to them.