Directly, before ill. End of life decisions are extremely important in people of all ages and health conditions. The best way to approach these matters is directly - it is important to discuss these matters open and honestly with our close family members. Printing out advanced directive paperwork to discuss (and review, sign, & witness) is a good place to start this conversation. Hospitals have staff to help with ad's.
Ask. Choose proper time & moment & mention others like friends or family & try to get herfeeling & wishes. Mention cases where people did not have directives & became subject to measures they would have otherwise declined or consented.