Paul is tested by the Bene Gesserit Reverand Mother. In a very famous scene from early in the novel, one of the Bene Gesserit Reverand Mothers (Charlotte Rampling) comes to test whether or not Paul is a "human." This involves putting a poison needle at his neck called the Gom Jabbar, while his hand is inserted into a box that simulates pain. If he pulls his hand out of the box, he dies.
Duke Leto Atreides and Gurney Halleck. Duke Leto (Oscar Issac) is Paul's father and the leader of House Atreides. He has been tasked with taking control of the planet Arrakis, better known as Dune. Gurney Halleck (Josh Brolin) is one of Leto's most trusted friends, and also the person who teaches Paul how to fight. In the 1984 Dune, Gurney was played by Patrick Stewart.
Lady Jessica makes it all happen. Paul's mother, Lady Jessica (Rebecca Ferguson) is also a member of the Bene Gesserit order. You can think of them as Space Witches crossed with Jedi, if you want. But, Jessica is more pivotal than simply being the mother of the hero. By the end of the book, you realize, in some ways, she's behind everything.
Liet-Kynes is the secret to the revolution. In the original novel, the character Liet-Kynes was a man. But now, the character has been reimagined as a Black woman, played by Sharon Duncan-Brewster. Like many characters in Dune, Liet-Kynes isn't what they seem to be at first. Although she appears to be working for the Emperor, Liet-Kynes is the person who can connect Paul with the Fremen, and help him start a revolution.
Don't mess with Stilgar. If you think that Dune seems top-heavy with formidable warriors and badasses, you're not entirely wrong. In the new film, Javier Bardem plays Stilgar, the de facto leader of the Fremen. Because the Fremen are the natives of Arrakis, Stilgar is the person who knows more about the deserts of Dune than anyone else. He's also the one person who makes a pivotal decision about Paul and Jessica that changes everything.
Duncan Idaho versus everybody. The best swordsman in House Atreides is the heroic Duncan Idaho. In the new Dune, Jason Momoa is playing perhaps the most enviable role in the entire saga. Not only does Duncan have a memorable (if small) role in the first Dune novel, he actually returns for all the other installments. Saying exactly how and why Duncan becomes so important would also be a spoiler.
Worm Sign! The Sandworms of Arrakis are a pretty big deal in Dune. Without these alien animals, the valuable substance of "the Spice" would not exist. The Sandworms are huge, and learning to ride them, and master them is just one of many things Paul has to face. Like the story of Dune, the Sandworms are neither good or evil. But, they do change the story in unexpected ways, well beyond the Spice.