I'm interested in learning more about Metta Meditation, and wondering if there are different approaches to this style of meditation.
I understand that the history of this practice is quite long, and it would be difficult to be comprehensive, but for the sake of brevity an answer could include only broad differences in approach. Or is there generally only one style of practice?
I am not so knowledgeable about answering this question. My impression is, at least the Pali Suttas, do not contain many approaches to metta meditation.
Some basic Pali Sutta passages about metta, in increasing detail, are:
Meditate on love. For when you meditate on love any ill will will be given up.
Seeing that the hindrances have been given up in them, joy springs up. Being joyful, rapture springs up. When the mind is full of rapture, the body becomes tranquil. When the body is tranquil, they feel bliss. And when blissful, the mind becomes immersed.They meditate spreading a heart full of love to one direction, and to the second, and to the third, and to the fourth. In the same way above, below, across, everywhere, all around, they spread a heart full of love to the whole world—abundant, expansive, limitless, free of enmity and ill will.
In Theravada Buddhism, Chapter IX (page 291) the Visuddhimagga is a popular manual.
Here's Buddhas instruction on how to be complete in Metta meditation.
"Monks, for one whose awareness-release through good will is cultivated, developed, pursued, handed the reins and taken as a basis, given a grounding, steadied, consolidated, and well-undertaken, eleven benefits can be expected." -- Metta Sutta
We cultivate good will. The easiest way to cultivate and develop metta is by chanting a mantra. The Karanya Metta Sutta contains a Pali verse which signifies the essence of metta.
sabbe sattā bhavantu sukhitattā
May all beings be happy at heart.
This is the Pali mantra. Best time to chant the mantra is early morning when we are fresh. If you do this you will establish a base consciousness of good will that will be there for the rest of the day (if you don't do actions that go against good will).
The development of metta requires time and energy and a favorable environment. The best is association of bona fide monks who practice metta.
