Jane Austen's actually doesn't make use of a whole lot of different literary elements in her writing. Instead, Austen prefers a much more direct style, letting the story and the characters make her point. However, she does make use of a few literary devices in Sense and Sensibility, including foreshadowing and allusion.
One instance of foreshadowing can be seen when Marianne first meets Willoughby. It is no coincidence that Marianne meets Willoughby while ascending the downs behind Barton Cottage on a rainy day. The rain had let up enough to inspire both Marianne and Margaret to venture outdoors, but it starts raining again, leading Marianne and Margaret to run for the house, which is why Marianne twists her ankle and falls. Hence, not only does Marianne injure herself in the rain, but Willoughby also appears in the rain and carries her home in the rain. Since rain can symbolize dark emotions, it is clear in this instance that Austen is using the rain to foreshadow that Willoughby will not prove to be trustworthy and to foreshadow the pain he will soon cause her. Her sprained ankle likewise foreshadows the pain she will soon endure. In addition, As Austen describes, after seeing Marianne safely home, "[Willoughby] then departed, to make himself still more interesting, in the midst of a heavy rain" (Ch. 9). His departure into the rain portrays him as a very dark and mysterious figure, despite how charming and handsome he appears to be at first, which further foreshadows the discovery of his untrustworthy nature and the heartbreak he soon gives Marianne.
Allusion is when an author makes a reference to another piece of literature. After Willoughby announces that he is leaving for London, leaving Marianne brokenhearted, Austen makes a very interesting reference to Hamlet. Several days after he has left, Mrs. Dashwood, also missing Willoughby, picks up a book of Shakespeare and sadly remembers, "We have never finished Hamlet, Marianne; our dear Willoughby went away before we could get through it" (Ch. 16). Hamlet is an interesting allusion for Austen to make in the book since, in the play, Ophelia is driven insane by Hamlet. Hence, not only is the reference to Hamlet an allusion, it also foreshadows Marianne's illness, which was the result of Willoughby's treatment of her.