Metta is often practiced by silently repeating several phrases directed initially at oneself, and then successively to a benefactor, a friend, a netural person, a difficult person and to all beings. Ayya Khema's phrases, suggested by the words of the Buddha, are as follows:
May I be free from enmity.
May I be free from hurtfulness.
May I be free of troubles of mind and body.
May I be able to protect my own happiness.
May you be free from enmity.
May you be free from hurtfulness.
May you be free of troubles of mind and body.
May you be able to protect your happiness.
May all beings be free from enmity.
May all beings be free from hurtfulness.
May all beings be free of troubles of mind and body.
May all beings be able to protect their happiness.
In German, these are as follows:
Möge ich frei sein von Feindseligkeit,
möge ich keinem Wesen Leid zufügen,
möge ich frei sein von Schmerzen in Geist und Körper,
möge ich fähig sein, mein eigenes Glück zu behüten.
which in English could also be translated as:
May I be free from hostility,
may I cause no harm to any being,
may I be free from pain in mind and body,
may I be able to protect my own happiness.
Often today, different phrases are taught, such as
May I/you/all beings be happy.
May I/you/all beings be healthy.
May I/you/all beings be safe.
May I/you/all beings be peaceful.
What's most important is to use phrases that are meaningful to you - and not too complex; simple is better.
But do notice how much easier it is to say the original pharses to someone you have great difficuly with - for example your least favorite politician or a terriorist. It might be quite difficult to wish that very difficult people be happy, healthy & safe (maybe you can do the peaceful phrase). But certainly you can wish they be free of enmity and hurtfulness. And you certainly can wish that those very difficult people be free of troubles of mind - after all, then they would not be so difficult. And maybe their difficulty stems in part of from troubles of body, so maybe you can do that part as well. And when you understand that the only happiness that can be protected is that which is generated via wise and wholesome actions, you can even wish difficult people have happiness that can be protected.