In order to empathize with the suffering of others, make mental images. When someone experiences suffering and pain, make a picture in your mind as if it were happening to you. Whatever you would want other people to do for you in such a situation, you should do for others.
This is the way to master the attribute of compassion and sharing the burden of others. Compassion may cause us a bit of pain, but it enables us to alleviate the far greater pain of others. Because when someone sees that you are suffering with him or her, it helps alleviate some of their pain.
Today, think of someone you know who is in great pain. Then ask yourself how such a person would most appreciate your help.
(see Rabbi Simcha Zissel Ziv - Chochmah Umussar, vol.1, p.2)