arsenic kisses - Writing

I don't post often, so I don't expect many people to see this and give it much more than a half a thought, but I plan to be working on a non-fiction book over this coming summer. I enjoy writing, recreationally, and have been told in the past that my expository writing is nothing to be ashamed of. This, however, is new territory.

My grandfather lived a hard life. He did quite well for himself in the end and was a wonderful person. He passed away just over four years ago, and had seen the end coming. He began dictating a book about his life, but never finished. The manuscript, what of it there is, is in a binder at my family's house. I've read it. He was elderly and ailing, and there are gaps in the continuity.

I'm going to need to conduct interviews, and learn how to organize notes when it comes to writing that requires I deal with people. I do not really know how to do this. So, anyone who sees this and has some advice, please.