If you've ever had a friend who knew he or she had a terminal illness and that death was coming soon, you know how difficult it can be to know what to do or say. The most important thing to remember is that the person is still living, so always be as respectful as you would if this friend hadn't told you about the disease. Try to focus on the here and now rather than the person's impending death.
Some people avoid anyone who has a terminal illness because they don't want to be depressed or think they might catch whatever it is. Chances are, unless the afflicted person has been quarantined, it's not contagious.