It's hard to squeeze Dune into a single movie. The book is a good 500 pages long, which fits better into three movies than into one. But if you are determined to fit it into a single movie, it should be possible. Here's one way:
ACT 1 (30 min) Start in Arrakeen, with the Atreides already in charge. Leto is the kind master, Paul his formidable young son. Their rivals are the Harkonnen, a nasty bunch (they abuse servants). Introduce Arrakis as the source of the Spice, possibly as part of Jessica's training of Paul in esoteric disciplines. The Fremen are mentioned, but as a minor impoverished rabble. Meanwhile, the Emperor, the Space Guild, and the Harkonnen meet and agree to replace the Atreides in order to maintain control of the Spice. The Harkonnen attack, Leto dies, and Paul and his mother flee to the desert. End with Paul looking back and vowing revenge.
ACT 2 (30 min) Paul and Jessica encounter the Fremen, and are taken in by them. Paul tests himself against young Fremen fighters and is impressed; they are very good, but he is better. He accompanies them on a raid against the Harkonnen, and is again impressed. He joins the Fremen, and becomes a worm-rider. He learns the true size of the Fremen from seeing one of their secret meetings. Jessica speaks of the Voice from the Outer World prophesy. Following Jessica's advice, Paul decides to lead the Fremen against the Harkonnen. Meanwhile, the Harkonnen are making a cruel mess of Arrakis.
ACT 3 (30 min) Paul campaigns to become the Fremen war-leader. This effort is shown as a montage of knife fighting and speeches before increasingly large gatherings. Harkonnen cruelties continue. The Emperor announces plans for a visit. Paul, Jessica and Stilgar begin training the troops, incorporating her and Paul's esoteric training. They wait for a sandstorm and attack in force with wormriders. Fight scenes between Fremen and Hakonnen. The fight goes to the Fremen. The Emperor flees in a ship. Paul addresses the crowds of Arrakeen from a balcony proclaiming a new day on Arrakis, with the natives in charge.
I think that could work. But some elements does get left out, given the compressed time-line: the spice as a mutagen, the nature of the Bene Gesserit and their goals, the Kwisatz Haderach, Paul's Harkonnen heritage, Paul's duel with Feyd-Rautha, and everything about Liet-Kynes.