Jot down what you remember about each chapter, section, or even paragraph. If your reading comprehension is already decent, you may only need to take occasional notes.
Don't rewrite the novel. On the other hand, don't write so few notes that you can't follow what was going on chronologically in the story at a given point.
Anytime a major event happens, or a new character is introduced, or some odd detail sticks out, write it down in your notes.
Try writing down characters and their relationships on one page and a basic time line for the story on another page. Draw a family tree, if it helps.