Buddhist teacher, author, and nun Pema Chödrön gives tonglen instruction as follows:
"On the in-breath, you breathe in whatever particular area, group of people, country, or even one particular person – maybe it’s not this more global situation, maybe it’s breathing in the physical discomfort and mental anguish of chemotherapy; of all the people who are undergoing chemotherapy. And if you’ve undergone chemotherapy and come out the other side, it’s very real to you. Or maybe it’s the pain of those who have lost loved ones – suddenly, or recently, unexpectedly or over a long period of time, some dying. But the in-breath is – you find some place on the planet in your personal life or something you know about, and you breathe in with the wish that those human beings or those mistreated animals or whoever it is, that they could be free of that suffering, and you breathe in with the longing to remove their suffering.
And then you send out – just relax out – send enough space so that peoples’ hearts and minds feel big enough to live with their discomfort, their fear, their anger or their despair, or their physical or mental anguish. But you can also breathe out for those who have no food and drink, you can breathe out food and drink. For those who are homeless, you can breathe out/send them shelter. For those who are suffering in any way, you can send out safety, comfort.
So in the in-breath you breathe in with the wish to take away the suffering, and breathe out with the wish to send comfort and happiness to the same people, animals, nations, or whatever it is you decide.

Do this for an individual, or do this for large areas, and if you this with more than one subject in mind, that’s fine… breathing in as fully as you can, radiating out as widely as you can."