There are many different ways to begin the planning ahead conversation. You know your family and how your loved ones might best respond to the topic. For some families, it might be a casual conversation over dinner or another family gathering. For other families, a formal meeting might be better suited.
Regardless of your approach, the conversation is much easier to have when death is not imminent. Discussing the subject with loved ones earlier in life when they are younger, and most likely healthier, makes the topic easier to talk about and keeps the focus on the celebration of life rather than an impending loss.