The original name of this practice is metta bhavana, which comes from the Pali language. Metta means ‘love’ (in a non-romantic sense), friendliness, or kindness: hence ‘loving-kindness’ for short. It is an emotion, something you feel in your heart. Bhavana means development or cultivation. The commonest form of the practice is in five stages, each of which should last about five minutes for a beginner.

In the first stage, you feel metta for yourself. You start by becoming aware of yourself, and focusing on feelings of peace, calm, and tranquillity. Then you let these grow in to feelings of strength and confidence, and then develop into love within your heart. You can use an image, like golden light flooding your body, or a phrase such as ‘may I be well and happy’, which you can repeat to yourself. These are ways of stimulating the feeling of metta for yourself.
In the second stage think of a good friend. Bring them to mind as vividly as you can, and think of their good qualities. Feel your connection with your friend, and your liking for them, and encourage these to grow by

repeating ‘may they be well; may they be happy’ quietly to yourself. You can also use an image, such as shining light from your heart into theirs. You can use these techniques — a phrase or an image — in the next two stages as well.

Then think of someone you do not particularly like or dislike. Your feelings are ‘neutral’. This may be someone you do not know well but see around. You reflect on their humanity, and include them in your feelings of metta.
Then think of someone you actually dislike — an "enemy", traditionally— someone you are having difficulty with. Trying not to get caught up in any feelings of hatred, think of them positively and send your metta to them as well.
In the final stage, first of all you think of all four people together — yourself, the friend, the neutral person, and the enemy. Then extend your feelings further — to everyone around you, to everyone in your neighbourhood; in your town, your country, and so on throughout the world. Have a sense of waves of loving-kindness spreading from
your heart to everyone, to all beings everywhere. Then gradually relax out of meditation, and bring the practice to an end.
Listen to or download full guided introductions to the Metta Bhavana.