The key is to be attentive and document. You could write down their stories as they tell them or use a voice recorder. Also, collecting important objects related to their life and attaching stories to them is a great idea. These combined approaches ensure that their life story is well-preserved.
You can start by having regular conversations and recording them. That way, you capture their memories and experiences in their own words.
Well, one good way is to create a photo album along with written notes about the events shown in the pictures. Another option is to make videos where they share their stories. Both methods help preserve those precious moments and tales for a long time.