I was brought up with a very scientific and rational background and education, and the ability to heal other people at a distance has been one of the hardest things for me to understand and accept. Yet I have seen it and experienced it too often to doubt it any longer. And there are interesting scientific studied that confirm the healing power of prayer and visualization.*
In my experience, I've found that the best way to work on healing is to picture myself as a clear channel for healing energy, and envision the spiritual energy of the universe flowing through me to the person who needs it. I think of my higher self sending energy to the other person's higher self t support them in whatever they need to do to heal themselves, keeping in mind that it's okay if the person chooses not to get well. At the same time, I picture the person as he or she truly is ... a divine being, a beautiful and perfect expression of God ... naturally healthy and happy.
*See Healing Words - The Power of Prayer and the Practice of Medicine, by Larry Dossey, M. Visualization.