Gil Fronsdal provides an excellent introduction to the four positive qualities of the heart known as the Brahmaviharas. The four qualities, lovingkindness, compassion, appreciative joy, and equanimity are also known as the four immeasurables, because they can be extended to all beings without measure. The article includes a brief discussion of the use of meditation to cultivate those qualities. You can find his article here: The Four Faces of Love: The Brahma Viharas.
Melvin Escobar provides a description of metta, a meditation practice that can help us to open to the Brahmaviharas. His article includes a number of suggested phrases that express intentions you can explore. You can find his article at this page: Loving-Kindness: May All Beings be Happy