A. The Force Awakens
Rich McCormick in Verge has argued that "Star Wars: The Force Awakens" broke internet records because of its minimalist trailer, i.e. by removing the voice over that says "In a world..." and by hiding the major plot points:
The Force Awakens' clips showed impressive restraint in an age where two minutes are jammed with as much exposition as producers can throw at the screen, pulling back on the amount of detail and building excitement by deliberately avoiding major plot points....The first teaser for The Phantom Menace's first teaser dropped the dulcet tones of the "in a world..." voiceover man, relying instead on carefully selected shots that Star Wars-starved fans could pick over again and again. In the process, it broke the internet before breaking the internet was a thing people aimed to do. The Force Awakens, again, bucked the trailer trend by omitting the kind of information that most trailers include as standard, and spawned thousands of feverish fan reaction videos, posts, and discussions.The Force Awakens can afford to do so, in the same way that IBM and GE need not write "International Business Machines" or "General Electric". IBM and GE has already spent millions of dollars in building its products and advertising them for several decades that their logos or initials are already well recognized icons of their respective companies. Similarly, the Force Awakens was built on the foundations of 6 Star Wars movies by George Lucas which are all blockbusters. A fan watching the trailer would already see parallels in the previous movies: Rey and Luke, R2D2 and BB-8, Darth Vader and Kylo Ren. The fan is already assumed to know the force, light saber, Jedi, Dark Side, and Storm Trooper. With these data, the fan can already make connections and try to deduce the major plot points, which builds up the excitement to watch the movie.
B. Shawshank Redemption
But what about an ordinary movie like Shawshank Redemption? The first word of the title is already a marketing headache since it does not conjure anything familiar. There is no Shawshank Prison as prequel that the reader can spring from to make sense of the Shawshank Redemption. With these handicaps, the trailer has to reveal major plot points to give the viewer what the movie is all about: the court verdict, the life in the prison, and the theme of hope. But even then, the film never became a blockbuster in the cinemas; it was only later that the movie was found to be exceptionally good. Had it been shown in today's era of blogs and social media, it would have a fair chance to be a blockbuster in cinemas, too:
Despite its box office disappointment, the film received multiple award nominations (including seven Oscar nominations) and outstanding reviews from critics for its acting, story, and realism. It has since been successful on cable television, VHS, DVD, and Blu-ray. It was included in the American Film Institute's 100 Years...100 Movies 10th Anniversary Edition. It is now widely considered one of the greatest films of all time. In 2015, the United States Library of Congress selected the film for preservation in the National Film Registry, finding it "culturally, historically, or aesthetically significant". (Wikipedia: Shawshank Redemption)
C. Lord of the Rings
A trailer must tell what the film is all about: the setting, the characters, and the conflict. How the film will try to resolve the conflict, the trailer can leave out. In the same way, when marketing a book, the setting, the characters, and the conflict must be spelled out in the book's marketing copy at the back cover. Here is an example from the Lord of the Rings:
In ANCIENT TIMES the rings of power were crafted by the Elven-smiths and Sauron, the Dark Lord, forged the One Ring, filling it with his own power so that he could rule all others. But the One Ring was taken from him, and though he sought it throughout Middle-earth, it remained lost to him. After many ages it fell by chance into the hands of the hobbit Bilbo Baggins.Notice that the first three paragraphs of the marketing copy reveals the setting, the characters, and the conflict. The third and fourth paragraph describes the major plot: it is a quest to Mount Doom to destroy the Ring. Whether Frodo and company would accomplish the quest is left for the book to tell. Also, the copy reveals something intriguing through the word "mysterious". All these creates a tension or a cliff-hanger that needs to be resolved by reading the book.
From Sauron's fastness in the Dark Tower of Mordor, his power spread far and wide. Sauron gathered all the Great Rings, but always he searched for the One Ring that would complete his dominion.
When Bilbo reached his eleventy-first birthday he disappeared, bequeathing to his young cousin Frodo the Ruling Ring and a perilous quest: to journey across Middle-earth, deep into the shadow of the Dark Lord, and destroy the Ring by casting it into the Cracks of Doom.
The Lord of the Rings tells of the great quest undertaken by Frodo and the Fellowship of the Ring: Gandalf the Wizard; the hobbits Merry, Pippin, and Sam; Gimli the Dwarf; Legolas the Elf; Boromir of Gondor; and a tal, mysterious stranger called Strider.
The principle of "less is more" for movie trailers is only for those who have already invested more in marketing in the prequel movies. But for films who have just built their fictional world out of nothing and who has only one chance to convince the customer to view it, the marketing principle should be "more with less" for the trailers--more revelations of major plot points in less number of minutes.