"You've always been a cunning linguist James" - Miss Moneypenny to James Bond in The World is Not Enough.

Good sex should involve all the senses - sight, touch, taste, smell and hearing.  Oral sex directly involves the taste of a woman's pussy juice (and a man's spunk)  as well as close-up smell and vision and exquisite feel for both giver and receiver - is it not then a fundamentally important part of sex?  It is in my opinion also the most intimate part of sex, one that creates trust between giver and receiver.

Cunnilingus is the stroking, tickling, proding and sucking of a woman's vulva with one's tongue and lips.  Most women greatly enjoy it (a recent Cleo magazine poll found 90% of their readers enjoy receiving it) and there are many who say they get their best orgasms from it.  Additionally most women expect to receive it from a sexual partner so it is worthwhile developing one's skills at it.  Although it is usually regarded as the final stage of foreplay before intercourse, it can also be a complete act in itself, such as during a lunchtime rendez-vous in an office or in a secluded area of a park. Along with fellatio It can also be the option for sex when condoms aren't to hand.
How a woman feels about oral sex is likely to be determined by her sexual experience generally.  If she's well experienced she is more likely to be a fan of oral sex, both giving and receiving, than if she isn't. If her experience is limited to a few partners who have either been unenthusiastic performers of oral sex, or maybe even totally unwilling, then you will need to be subtle in your approach to the subject. Don't take it for granted that while you are kissing and caressing her nether regions that she will want or expect you to move to her treasure box.
The issue is obviously to the fore with a new partner, so much so that I think in most cases it is better to postpone the topic to the second time you make love. In any event find out first by asking her if you can go down on her. The right moment for the request is important and there are really no precise guidelines I can give as to when to ask the question is; you have to rely on your instinct. It might be when you're sitting together in a club; when you're on the sofa or the bed or when you have just  kissed your way along each of her innner thighs. There are some rules about how to pose the question:

* Make it sound that you really want to give her pleasure
* Don't imply "I'll do you if you'll do me"
* Ask as seductively as you can; a whisper in her ear is good; or if you are already in position an inquiring look may be enough.
This view shows a woman's unstimulated vulva as it would look after you have removed her panties.
After some stimulation both the inner and outer lips become more puffy and you can see the entrance to the woman's vagina at the bottom.
Cunnilingus should be the natural extension of foreplay - kissing, stroking nibbling and caressng other areas, getting her in the mood for receiving oral sex.