Reflecting on your good qualities, remembering times in your practice when you saw these beneficial qualities arising, learning how to appreciate the good qualities and what enabled you to do them, learning to take joy with yourself. Learning how we can then reflect on the good qualities of others, realizing that it's these good qualities that will enable them to end their suffering.
Many times it's easier to do Compassion/Lovingkindness than Sympathetic Joy meditation because it's no threat to us. Sometimes we see other people's good qualities as a threat to our sense of self-worth. However, if we understand that it is these good qualities that will fulfill our Compassion/Lovingkindness wish, then that tends to break through the jealousy or the envy or the creating of competition. This can make us feel joy by allowing ourselves to appreciate other people's beneficial qualities. When doing the Compassion/lovingkindness, we often think of the suffering of others, which doesn't tend to threaten us so much if we have a negative self image because we are thinking of other people's suffering.
But when we come to Sympathetic Joy, it is often very difficult for Westerners because of the conditioning in society of competition, to compete with others, to compete with ourselves, trying to prove that we are okay in society or to whomever they believe they must proof themselves to. There's not a lot of encouragement to believe in our beneficial qualities and take joy in them. So sometimes, when we are getting into trying to practice Sympathetic Joy, thinking of the good qualities of somebody else, we may find some resistance.
Often I will start the Sympathetic Joy by asking you to remember how you felt when someone expressed a genuine appreciation for something you did or an appreciation of your beneficial qualities and how it felt good to you. By remembering that feeling when someone acknowledges your goodness and then asking yourself to allow that same level of appreciation for yourself at that time because you have already seen someone see those beneficial qualities in you, we try to bring up that same sense of appreciation in ourselves, knowing how good it feels when someone acknowledges the good qualities in you.