1. Sit upright, but in a comfortable posture

2. Take a few deep breaths

3. Think of yourself, or if that is difficult someone very close to you, who brings up a natural sense of kindness or gratitude. 

4. Mentally repeat a phrase wishing yourself, or another, happiness. Some suggestions are: may I be happy, may I be peaceful, may I be well, may I meet with success, may I be healthy and strong, may I have the clarity of mind to overcome inevitable difficulties, problems, and failures in life. 

5. Continue this process for a few moments, with sincerity. 

6. If the mind wanders to another person, wish that person happiness and move back to the person you were thinking of previously. 

7. After oneself, or the person who most brings up a sense of kindness has been wished well, move to another person who one respects highly such as ones parents or spiritual guide, and continue that process of wishing them well described above.

8. After this person has been wished well continue in order of decreasing amount of personal affection. Some examples may be wishing well for ones parents, spiritual teachers, brothers and sisters, extended family, close friends, acquaintances, colleagues, people who you have just met in passing, people who you have not personally spoken with, people who have annoyed you, people with interests adverse to your own, people who actively attempt to harm you, and finally all people, animals, and creatures on the planet.

9. Extend the same care and kindness to all persons or classes you visualize. 

10. Once you have wished kindness to all living beings in the planet, extend throughout boundless space. Make this mind state expand to cover the entire universe of possibility within your mind without distinctions. 

11.  Allow the mind to abide in this state of expansive kindness for as long as you plan to sit in meditation for. As always, when the mind gets distracted bring it back to whatever stage of practice you were in (whether thinking good for ones close ones, or the entire universe). 

Tips:

If visualizations occur, welcome them and be aware of them without getting distracted with their content. For example if the feelings that arise during this meditation are associated with imagery, focus more on the positive feelings than the content of the imagery. 

Once you have practiced this for a while, experiment without the regimented order, allow the mind to wish kindness to whatever person or group of person it is inclining to, so long as the wish for kindness is sincere and the feelings generated by the thoughts are positive.

It is easier to do this in a quiet space with oneself or others but also try this practice in large groups of people, in airports, in the bus.