Three specific literary devices are used in the movie version of Ethan Frome by Edith Wharton, and all three of them are also used in the novel. The use of a framed story, of flashback, and of foreshadowing are consistent in both literary works. How they are used in the movie, however, is often at least slightly different than how it is used in the novel.
Both the novel and the film utilize the literary technique of a framed story, which is simply telling a story within a story. In the novel, the narrator is an engineer who is in Starkfield for the winter on business; he is the one who assembles the pieces of this story and then tells the story to us. In the novel the narrator makes no claim that what he tells us is completely accurate; he admits it is his best guess based on what he has learned. He says:
I found the clue to Ethan Frome, and began to piece together this vision of his story.
In the film, the narrator is much more of a character, and he is a minister who arrives in town. We see more of his life, including a party thrown for him by his church, than we do the engineer, but the principle is the same. He sees the pitiful wreck of a man named Ethan Frome and then pieces together Ethan's story. This is necessarily a more definitive reality since we see it played out on the screen and the narrator never hints that this story is just what he has surmised or envisioned.
Flashback is necessarily a part of a framed story, as the primary narrative must all be told in flashback. That is true in both the novel and the movie. In the novel we learn just a bit about Ethan's one-time dream to be an engineer as a student in Florida; when we see that on the screen it is a bit more real and therefore his reality in Starkfield this winter becomes much more, well, stark. When the second story begins, Ethan is already married to Zeena and Mattie is already living with the Fromes; without the literary device of flashback, we would never learn how and why those two things happened.
Finally, the use of foreshadowing is also used both in the novel and the movie. Unfortunately, like most movies (in my opinion), the foreshadowing is often overly obvious. In fact, Madden feels the need to insert a foreshadowing scenario not found in the novel in which Maddie rather weakly attempts to commit suicide with the poison she finds in the barn. The novel's foreshadowing of the "smash-up" at the end of the novel is the early, more subtle revelation that another couple nearly smashed into the tree accidentally while sledding. This addition to the story is not only treating the audience as too inept to catch subtlety but it also distorts Mattie's character. She is just not that morose or desperate until the very end of the novel.
One other small literary device which is used effectively in the movie is the use of the colloquial dialect. It is brusque and terse and rather clipped, and hearing it reminds us that these characters are just as stilted on the inside (emotionally) as they are on the outside.