You've gotta figure out if they like hot talk, dirty talk, or complimentary talk.
Example hot talk, during doggy "Baby .... even if you werent so tight ... even if you werent so wet ... i could cum just watching big big cock disappear into your sweet body"
Complimentary talk: Some just love the compliments, "Fuck youre so tight", "God you feel so good", "Baby your body is gonna make me cum so hard"
Dirty talk: "You like that? Only a dirty little whore gets THIS wet on her back talking a big cock. Say it whore -- who does this cunt belong to now? That's it -- if you cum on my cock I'm gonna cum wherever the fuck i want".