If you didn’t get a chance to write your magnum opus while you were on this side of life, you could write it from the other side, through mediumship. Here is an article about a book that was written this way, by W. T. Stead, called The Blue Island.  Stead was on the Titanic, and in the book, he talks about the transition with the others who were also on the ship. It also has an an introductory letter by Sir Arthur Conan Doyle. The article has a google books link, which allows you to read through the various parts of the book, but the book itself is not free. I read portions of the google info, and I thought it was interesting enough for a full read. If you’d like to pick up a copy, you can get it here.