Explaining backstory before the main narration is a common movie and book device. Because exposition can interrupt the flow of the story, background story often appears in an opening sequence or a prologue. It does not have to operate within the confines of the plot, so the author can tell it in a straightforward manner. The Star Wars movies feature an iconic expository device; the yellow lettering text that scrolls up the screen before the movie begins is an introductory type of exposition.
One of the weaker exposition tricks involves having two characters explain to each other something they already know to provide the audience with the same information. Sometimes referred to as "Maid and Butler dialogue," this technique is an old play device featuring the maid and butler discussing backstory. These characters have no other reason to speak this way to each other, and it can make for awkward dialogue.
A common way to work expository dialogue into the story involves the introduction of characters that need facts explained to them. This device requires someone (often, the main character) who is new to the situation. The movie "The Matrix" takes advantage of the character Neo's being new to the real world by having him ask questions and having other characters explain things to him.
A scene in a movie or book can describe events that have transpired. In the third chapter of "Harry Potter and the Half Blood Prince." author J.K. Rowling describes Harry's room while he is sleeping. The description mentions trash strewn around, indicating that Harry is messy and spends most of his time in his room, and quotes several of the newspapers laying around the room. Rowling describes an empty trunk in the middle of the room, which informs the reader that he intends to pack the trunk but has not gotten around to it. We learn more later, but this descriptive scene tells a great deal about what has happened since the end of "Harry Potter and the Order of the Phoenix" without using dialogue.