In order to take a Formalist critical approach to Jane Austen's Pride and Prejudice, you will need to examine and analyze the parts in the following Formalist categories: character; figures of speech, which are techniques of literary devices that are expressive instead of being plain prose (e.g., sarcasm, metaphor, synecdoche, etc.); imagery, which is sensory related description; plot, which is all the events, etc. that organize the storyline (e.g., inciting action, falling action, conflict, etc.); point of view, which is the perspective of the narratorial voice (e.g., 3rd person limited, 1st person, unreliable, etc.); setting, which covers atmosphere, historical era, mood and physical place(s) (e.g., time, flashbacks, fragmentation, etc.); and theme, which is the primary message or idea of the text. Identifying these literary elements and techniques, which both fall under the broader term of literary devices, requires what Formalists call "close reading," a reading in which the text is attended to on all levels form punctuation to grammar to syntax to vocabulary to idea, paragraph, section, chapter, etc, choices and arrangement.
In Pride and Prejudice, Austen's main character's would be described as primary and secondary protagonists (the former being Elizabeth and Darcy, the latter being Jane and Bingley), who are well-developed and dynamic, which means they are growing and changing, which is displaying what is called by some "character development." Austen's secondary characters like Mrs. Bennet, Mary and Mrs Lucas are static, which means they do not display character development, which is growth or change. The antagonists, Miss Bingley, Lady de Bourgh and sometimes Mr. Collins, are round (i.e., well-developed) but trapped within their own limited personalities and world views; they are not flat, which means under-developed, not representative of realistic persons.
[Below are some reliable academic links to detailed information on Formalist critical theory, including information from the Writing Center at Armstrong Atlantic State University, from which I drew parts of this Answer.]