Somethings are best kept simple, there is no need to find the “right thing” to say because when it comes to sexy talk, all you have to do is say what you’re thinking. If you notice how good any part of her looks, say it. If you want to go down on her, tell her that. Then you can describe little things while you’re doing it, say how much you like the way she tastes, how her bush feels against your face. How you want to put your tongue inside of her. If you want her to squeeze you tighter, take you deeper, use her spit on your dick, give the instruction. The more natural your sexy talk is, the more comfortable you’ll feel saying it, and that will come across to her. You can even start with a whisper in her ear, really any sort of honest comment or instruction comes off hot during sex. Don’t stress, and do it.