Is there anything more interesting than real life? Not to me. I love real life stories. From the time I was young, the biography shelf of the children's section in the library was my favorite. There was a series targeted to kids, and I read them all. Fantasy bores me. Give me a solid memoir any day. I like to know what people eat for dinner, where they work, where they go on vacation, all kinds of ordinary details that we all have in our everyday lives.
Writing it well in story form is the great challenge. When it's done right, you get Angela's Ashes by Frank McCourt. Or the Little House series by Laura Ingalls Wilder.
Sometimes you don't care about all that, you just want to get the information down in one place, in some kind of organized format to save it for posterity. Either way, we're talking lots of time and effort-- no easy task at all.
Where to start? With a collection of data: journals, letters, photographs, shopping lists, sales records-- anything saved that gives information about the life in question. You can start with a labeled box for your data, and later file and organize it. Collect it, keep it in one place, label and organize.