There are three elements of narrative voice that can impact the way a story is told.
Attitude has to do with emotion, values, beliefs, worldview, and feelings about a particular person or situation. The attitude of the narrative voice reveals how the narrator speaks, the narrator’s body language, his or her reactions, and the actions taken in a specific situation.
Attitude adds uniqueness to the narrator’s voice and provides deeper characterization. Consider how the phrase, “I can’t believe you two met online!” could change depending on who says it. A friend of the couple who is of a similar age and understands that various facets of online dating might say it with pleasant surprise, happy that their story worked out. An older relative who distrusts the internet might say it with derision and eye the boyfriend/girlfriend skeptically. In both cases, the reader is given further insight into the speaker.
Tone isn’t just what is said but how something is said, and it can completely change the meaning of the actual words. The phrase, “I’m sure you could,” can be supportive and kind when said in a soft and loving tone, or snarky and dismissive if the “sure” is emphasized in a spiteful tone followed up by an eye roll or huff of annoyance.
Speed of speech, loudness or quietness, word choice, emotion behind words, and physical actions accompanying words all affect tone. Keep in mind that not all body language and connotations are universal, so make sure that what you’re trying to convey with tone is understood by most readers.
Personal style (of the narrator not the writer) includes vocabulary, sentence structure, grammar and technical aspects, cadence, and personal preferences. This can be developed for each character to highlight uniqueness.
Be careful not to over do it with too much slang, jargon, or colloquialisms that reading the narrator’s dialogue or thoughts becomes a chore for the reader. Give just enough that the voice is recognizable to the reader when you switch narrators.