A few ways to cultivate Love, Compassion, and Bodhichitta:
Realize that the only enemy is the afflictions like anger, attachment, and ignorance. Beings are driven to madness by afflictions. If you think of it that way, you can't ever see anyone as an enemy. In fact, it's just the opposite. You feel pity for those who are sick with afflictions, even those who harm you. If you're going to identify an enemy, it can only be afflictions. Beings are controlled by the sickness of afflictions.
Since time without beginning, every being has been your best friend, mother, daughter, son, brother limitless times. Maybe they've forgotten they were your mother, but you remember because you understand rebirth. Maybe someone has harmed you in this life, but in limitless past lives they carried you in their womb, clothed you, fed you, and cared more about your health and happiness than their own.
Not one single atom has self-nature. Ultimately, there is no self or other. "Self" and "other" are only merely imputed by mind onto selfless forms. That's the meaning of all beings existing in name only. "I" and "Them" are merely labels designated onto compounded beings, designated by name. Not one atom of anyone is independent and permanent. Instead, every atom of every being is interdependent and impermanent. They have not even a speck of self-nature.