Are you reading by opening up to page 1 and reading through to the end? Don't do that. I know, I know, spoilers, but unless you're reading mysteries, it's not a big deal. The best fiction isn't just the ending. Everyone knows Captain Ahab dies at the end of Moby Dick, but that doesn't spoil anything.
So, read the first chapter. Read the beginning and end of the rest of the chapters – a few paragraphs, a page, something. Read the last chapter.
Analyze the story: make a list of characters and their relationships to each other. If there are people related to each other, make a family tree. Consider the locations: map them out, especially if they reference real world locations. Get a feel for how the story moves through the world. Tolkien's books are famous for including the family trees of his characters, timelines, and world maps. Do that.
Try reading a novel that's been made into a good film. Follow along reading and comparing the film adaptation to the novel. Something like C. S. Forester's book The African Queen and the 1951 film directed by John Huston.
Pick a novel that riffs on subjects you're already into. Sylvia Plath's The Bell Jar involves psychology as a major plot element, as do One Flew Over the Cuckoo's Nest and Requiem for a Dream. All three have been adapted into excellent films.