The Tonglen meditation of taking and giving is one of the advanced meditations in Lamrim. It's very powerful. It's effect is magnified when you combine the meditation with Equanimity. Tonglen is easier to begin when you think of family and those close to you. You already want to see them be happy and free from suffering, so imagining taking away their burdens and supplanting those burdens with happiness is easy and natural. It gets a little harder when you start imagining those people you are neutral about, the cashier at the grocery store or the barista at Starbucks, but with practice, you can grow your feelings toward them. The final hurdle is to bring your enemies to mind, those you carry resentments toward. You heart almost immediately closes, and it's tempting to digress into fantasies of revenge and actually take joy in their sufferings. But if you persist with Tonglen, it's like a hot torch melting your cold heart, and your feelings of anger, hatred, resentment, and the desire for retaliation melt away.