What are some examples of O'Brien's most important writing techniques (repetition etc.)?
An additionl technique he employs is actually repetition. He often repeats a phrase, or at times entire sentences or even passages, to achieve a few purposes.
First, in the case of "The Man I Killed" he repeats the description of the dead body to perhaps demonstrate to the reader how this image is affecting him. It gives the reader the sense that this is an image that will be forever burned in his memory, and by repeating the description he is also showing how a traumatic moment can replay itself in one's head over and over again, just as he is now doing for the reader.
Second, he uses repetition in the chapter "The Things They Carried". He continually says "they carried" to start sentences. This presents the information to the reader almost as a list, but also emphasizes the fact that these things were often burdens to them. By saying "they carried" repeatedly, that sense of weight and being weighed down is emphasized.
One important technique that Enotes discusses is the use of the third-person omniscient narrator. A third-person narrator means the narrator is an outsider looking into the story. Omniscience means that the narrator knows the thoughts and feelings of the characters. This is especially true for Lt. Jimmy Cross, as the narrator delves deeply into his thoughts and feelings. The narrator also uses limited third-person omniscience, too, when dealing with other characters.
Another technique O'Brien uses is flashback. The death of Ted Lavender is revisited several times throughout the novel through other characters.
This novel is an example of a composite novel, meaning it is made up of many different parts that could stand alone, actually, as separate short stories (O'Gorman). While the novel seems fragmented at times, it still blends because of the commonalities of the war stories.