Basic Instructions: Toward the bottom of the out-breath say "Suffering" aloud and then breath in Suffering. Toward the top of the in-breath say "Love" aloud and then breath out Love.
We generally recommend a spontaneous order for this practice, meaning that everyone is saying "Suffering" and "Love" aloud with their own breath cycle, rather than taking turns. The downside of taking turns is that you need an odd number of people in each group, in order not to be saying the same phrase everytime it comes around to you.
You can also add in a suggested visualization, to include the traditional element of Tonglen meditation, where on the in-breath one is inhaling a thick, dark cloud of suffering, and on the out-breath is exhaling a bright, radiating light.