The practice of Metta Bhavana - 'Cultivation of Metta (Goodwill or Lovingkindness)' is an incredibly powerful and important one. As I have said often, we can all agree that this world would be so much better if everyone else spoke and acted from a place of love - but you can't change anyone else. You can only change yourself. That is why cultivation of metta is so important.
The traditional form of Metta Bhavana goes back hundreds of years and follows the following rough outline: You practice cultivating metta for yourself, then for a (specific) friend, then for a (specific) neutral person, then for a (specific) enemy. Finally you practice expanding geographically to eventually hold feelings of lovingkindness and goodwill for all beings (the 'sending to the ten directions'). I emphasize 'specific' here because part of the power of the practice is that it avoids generalities. It is trivially easy to say 'I love all beings,' but much harder to find love for a specific person.
When you first start the practice it is common to see the progression from self to enemy as one of increasing difficulty, but this is a misconception that soon goes away after some practice. This misunderstanding is even repeated in the Wikipedia Article on Maitrī (Sanskrit for Metta):
The practice gradually increases in difficulty with respect to the targets that receive the practitioner’s compassion or loving-kindness. At first the practitioner is targeting "oneself, then loved ones, neutral ones, difficult ones and finally all beings,...While this is certainly how things feel at first, as we get deeper we realize that there are complications for all four people - especially for the self. It is often harder to generate love and empathy for our self than it is for the others - after all, we know all of our own faults and shortcomings.
We soon start to recognize that generating metta unconditionally is hard for the known and the unknown, the liked and the disliked (in other words the four persons used in the practice). And for me, the key person is the Neutral Person.
This may be a surprise to some of you, as very often the Neutral Person is skipped over or downplayed. There is surprisingly little written about the importance of the Neutral person in the practice. Even the name, neutral, has a connotation of being boring or unimportant.
We typically talk about them in terms of 'someone you would recognize but know little or nothing about.' They could be someone you pass on your way to work, or a cashier, or someone who sits in the corner at work (or Sangha) that you've never talked to.
The important thing is that you know nothing about them. They might volunteer at the Humane Society, or they might kick their dog when they get home. They might be open and generous or they might be bigoted and narrow-minded. The point is you don't know, and what you are practicing is to feel goodwill and love for them equally regardless of the truth of how they live their life. And that is hard. The Neutral Person can become the key, the pivot to your understanding of what it means for lovingkindness to be unconditional.
In the beautiful and well-known Karaniya Metta Sutta it says:
As a mother would risk her life
to protect her child, her only child,
even so should one cultivate a limitless heart
with regard to all beings.
The interesting thing here is that a Mother's love for her child is not unconditional - at least in the sense that it is dependent on the child being her own child. And yet we are told this is the kind of limitless heart we should be cultivating towards all beings.
Contemplating the Neutral Person is a powerful way to move beyond conditional love towards this unbounded heart. I have linked below a fully guided meditation where we focus on the Neutral Person - you are free to use it in whatever way helps you in your practice. If you have never practiced Metta Bhavana before, or if you need a refresher, this might be a good place to start.
Karaniya Metta Sutta: Good Will" (Sn 1.8), translated from the Pali by Thanissaro Bhikkhu. Access to Insight (BCBS Edition),
30 November 2013, http://www.accesstoinsight.org/tipitaka/kn/snp/snp.1.08.than.html .