First of all, simply be being there and listening to them when they want to talk, and letting them be silent when they want to be silent. Second, let them know its OK to feel what they are feeling. Thirdly, help them in practical ways, such as going grocery shopping for them or running errands. And fourth, learn from them. People who are dealing with death may sometimes be in more touch with their own mortality, which you may be able to learn from.