Per Cambridge Dictionary definition, empathy is "the ability to share someone else's feelings or experiences by imagining what it would be like to be in that person's situation".

It helps if I share the same experiences with that person or if I have been in the same situation. At the same time, each of us have different background and biases in our perceptions of any given experience or situation. That person's perception might be different (ever so slightly) than mine, but the shared experience helps me understand the feelings.

What about other people who I share little or no commonality?

To empathise, I ought to empty myself from preconceived notions and prejudices. I ought to make the time to get to know them and to know what they have gone through. To be intentional in my listening and to make the time to explore deeper and draw the essences of their experiences and feelings.

To empathise, I ought not be passive; I ought to engage and be present with the person I empathise. Sometimes it may take a few tries and that is okay.

See: Not any easier