In addition to frequent sybolism, as stated in the previous response, Shelley makes particular use of narration to divulge elements of the plot. Whenever Victor is particularly positive about a friend or family member, disaster is just around the corner. In Chapter 18, for instance when Clerval joins Victor, Victor describes him as "alive to every new scene, joyful when he saw the beauties of the setting sun, and more happy when he beheld it rise and recommence a new day." No one this happy lives long in this novel. Another good example is Elizabeth's letter in Chapter six regarding "little darling William" and his adorable "little dimples." I her very next letter, just a few pages later we learn that "William is dead!"
Shelley reminds us that Victor is narrating his story to Walden aboard the ship. Often, Victor uses apostrophe ("Oh, Henry!") and lets us know how terrible he feels about some later tragedy in the story. Victor has a wonderful memory and is precise about his account of events. It seems that he cannot help but give us some spoilers along the way, though.