To add to all the great suggestions above, one of my favorite things to do when distinguishing character voice is to figure out who in the story curses more. A buttoned-up nerd or bookish church mouse might not curse at all, finding dorky or antiquated replacement words. "Oh, fiddlesticks!" So it becomes a moment of character development when they utter their first real "fuck" on the page.
A brash person with little regard for their surroundings will curse even when it's unnecessary or inappropriate, and might have a smaller vocabulary than their peers because their favorite words all have four letters.
"Fucking gimme the thing."
"The what?"
"That little fucking thing. The buzzing thing. The shit you're holding right fucking now."
"Did you just forget the word 'vibrator?'"
"Fuck off."
Within a sex scene, one partner might say "yes please" while the other says "fuck yes" while the third is more "hell yeah" kind of dirty talker.
How someone curses, in the U.S. at least, can signify ethnicity or background without falling into racist caricatures. "Holy shit, you look awesome!" gives a different impression than "God damn you're looking good!" Or having a frustrated character say, "These fucking idiots are driving me batshit," feels different from, "These motherfuckers are about to drive me out of my god damn mind."