When my mom died, we found a spiral journal in a desk at their house. It was her book journal, with a list of books she'd read. Her list was dated (month and year when she read each book), and each title had a 1-2 sentence description of the book.
My siblings gave me the notebook--a treasure. I've enjoyed looking over it, and have gotten some ideas for "what to read next" from my mom's descriptions.
I also got inspired to keep my own book journal. Now I record title, author, and a 1-2 sentence description of each book I read. My journal's on the left in the picture; Mom's is on the right.
I finished a book last night, and this is what I wrote:
The Voyage of the Narwhal, by Andrea Barrett. Naturalist Erasmus Darwin Wells explores the arctic on a ship which meets with extreme circumstances. 19th c. romantic views of the Arctic is destroyed.