Its important to know that she may not be into you saying certain things so tread these waters carefully. Also, a good rule of thumb is if something feels awkward for you to say it is going to sound awkward so best not say it. Also, keep the tone and volume of your voice in check; saying things to loudly or with the wrong tone can come off in a wrong manner or in an awkward manner. As for what to say just tell her how much you like what shes doing or what you want to do to her in a more "dirty" manner.