I must have anticipated that question! What I just said is very helpful to develop more Equanimity towards others: "They are the owner of their own Kamma." You can develop this type of systematic thinking as we would with Compassion/Lovingkindness meditation. Also strengthening the fifth reflection is very helpful in developing more Equanimity, "To Care and Not To Care." This ties in with understanding that everybody is the owner of their own Kamma. To understand that no matter how we think things should be, or others should be, that's not going to change them, and we have to learn to accept the laws of existence. One thing is to develop a systematic reflection on what they call the "Three Characteristics of Existence." Reflecting more about impermanence, Dukkha and the last one, not-self. Especially in regards to the Five Aggregates. These five aggregates of this body and mind are often difficult to control. They have their own characteristics of impermanence, Dukkha and not-mine.
The body is not able to control sometimes, it follows its own nature, and so does the mind. Everybody has their own conditioning and their five aggregates. It's difficult to control our own, let alone somebody else's! So reflecting on "not me and not mine" is very helpful, because many people develop the idea that they can control others. But you can't even control your own body sometimes, you can't even control your own mind sometimes, so understanding that it is very difficult to control and change ourselves helps us to have more Equanimity towards others. We can try to influence others, but we cannot always change them, developing more Equanimity, to care and not to care. That also ties in with what I talked about in the beginning about knowing what one has power over and what one does not have power over.