It's not like in a porn movie - most women do not have an orgasm with in a minute or two. In Asia they call this cunnilingus technique "polishing her pearl. We have something like 5 times the nerve endings as men do "down there. Don't be afraid to give her clit a gentle massage with your tongue and lips as if you're calming it down just to get all worked up again. At Wal-Mart they have these little ice trays that make tubular ice for bottles. Think of your favorite food and pretend the pussy is just that.
Men, if you look like you are really enjoying yourself, too, it makes all the difference.
As a woman, the best thing I can say is, don't just start going at it! Don't forget about using the nose too! Get small pieces of what my husband and I now refer to as Cooter Ice. KNOW that it may take awhile! Just like BJs aren't that great if we take your pants off and deep throat you off the bat, we like to be teased with the idea for a while, and get really, really aroused before you get started. Definitely start off with light kissing and slow deliberate strokes of the tongue. Variation of pattern is also important.