The practice typically progresses through five stages: directing metta toward oneself, a good friend, a neutral person, a difficult person, and finally all beings equally. Practitioners repeat phrases like "May I be happy, may I be well, may I be safe, may I be peaceful and at ease."
Starting with oneself addresses the tendency to exclude ourselves from compassion. Many find extending kindness to themselves harder than extending it to others. The practice recognizes that genuine compassion for others requires not hating ourselves.
Moving through progressively challenging recipients—from friend to stranger to enemy—gradually breaks down the barriers we erect between "us" and "them." The goal is equanimity—caring equally for all beings' welfare without preference or aversion.
Research suggests metta practice increases positive emotions, reduces stress, enhances empathy, and may even alter brain structure. Beyond benefits to practitioners, it cultivates the fundamental Buddhist aspiration: may all beings be happy.
Source
Buddhist Meditation Tradition