ok, well
effort and time are two important factors. if you want to please the chick, you probably will. Things that help that are:
no alcohol. You'll both be less inhibited, yeah, but also numb. it numbs everything, including her nerve endings. be sober, but feeling sexy and relaxed.
don't be rushed. don't just attack her pussy- get comfortable, look at it before you dive in, smile like you can't believe you're gonna get to feast on it, and let her know YOU'RE enjoying eating it as much as she's enjoying it.
when you find something that she seems to really like... keep doing it. mostly to her clit. suck it, flick it with your tongue, lick it like its a tootsie roll pop and you're trying to find the center. just pay most of your attention to it.
use your fingers. Two. in and out. while you're sucking her clit. don't stop.