Cut your fingernails very short and make sure they are smooth to the touch. You can use your fingers to tickle her clitoris once in a while, or you use them to fill her (do this gently).
Also, if you're going to do be doing the oral sex with her laying on her back, you can reach up some times and lightly feel all over her body. Massage her breasts, feel her stomach, hold her hands. Change it up.
Also, I agree with the other posters. Let her know you enjoy it, take it slow, and ask her once in a while if you're doing it right. Just enjoy it.
