You know, I'd love to be able to write a step-by-step for this that always worked. Since nobody else has, I'd be assured of wealth. I am forced to admit, however, that my (limited) experience has shown that women vary greatly both across the population and over time in their preference for particular sorts of erotic stimulation.
Here's what I've generally observed to be true:
1) Don't start off anywhere near the clitoris. Yes, it's the love button. No, you can't make her happy by immediately going there. For an analogy, imagine that your intimate friend started off by petting the head of your penis and ignoring everything else. See? Too sensitive.
2) This is a learning experience. Chances are excellent that if you're asking questions like this, you have limited experience with this in general and with your partner in particular. Since all women are different, you're on a voyage of discovery every time you bed a new girl. This is one reason I was usually hooked up, but not a player in school - I wanted to have lots of fun with somebody, and it's just not possible to do that without getting up the individual learning curve of that particular woman. Corrolary: one-night-stands aren't the best loving.
3) Since it's a learning experience, you need to engage all your senses. Do the candle light thing so that you can see. Yeah, it's romantic too, but it's also highly practical. If you can't see, you won't learn anything from your eyes. Get your head down there even if you're not sure what to do with your tongue and lips. For one thing, your breath is arousing, for another, you can see what's there a lot better than you can feel it, and for a third, well, you should never put your tool anywhere you wouldn't put your tongue anyway.
She'll smell like her. That's fine. It's usually a strong scent, but not objectionable. You smell like you down there, too, and men are generally smellier... If she smells like the fish market at closing time, consider suggesting a coed shower (bet she was wearing pantyhose), or maybe you picked a dirty girl who'll give you a bigger gift than you wanted. Never, ever, ever tell a woman she doesn't smell as sweet as a spring breeze down there. Just adjust your choice of action to deal with the reality. If she's within ten days either side of ovulation, bathed today, and hasn't sweated much since, she'll smell female, but not unpleasant. The Japanese have the near-universal custom of bathing immediately before sex. I'm not a big fan, because I believe (like the French) that a woman should smell like herself instead of bathing supplies. If everybody's stinky, sweaty and smoky from clubbing or whatever, then the road to the bed should lead through the shower for both of you, preferably together. Believe me - there aren't many more fun things in the world than rubbing soap suds over a nude woman...
4) OK, so you're checking out the real estate. Presumably you've been stroking her torso, nuzzling around her breasts and neck, etc beforehand so she's already pretty enthusiastic. You kiss your way down her torso and put a hand flat between her navel and pubic bone. This is your seismometer. You'll feel when she takes a breath, and you'll feel when she squirms. Useful information. It's not a bad way to start off by kissing the insides of her thighs.
5) it's all about the personal variation: some women have small outer labia, some have big ones that obscure things. Some have an invisible clitoris, some have a large one (large here still pretty small). Some have a prominent hood, some don't. Don't worry, they've all got the same number of nerve endings somewhere down there, there's just variation in the distribution. Your mission is to find the nerve endings and make them happy.
Again, think about what feels good to your penis. soft, smooth and gentle is the order of the day, until she gets wound up and ready for more. Your mouth happens to be equipped with a decent lubricant which will do a good job softening your fingers. Oh, by the way - fingernails should be as short as you can stand and any pointy bits or rough spots should be filed down. Likewise, consider putting some massage oil or hand cream on to soften your manly callouses. You need to maximize your sense of touch, and to use the lightest caresses possible, especially when you get near the clitoris and inner labia.
6) If you find something she likes, she'll likely make a happy noise. The bad news is that most young women, most of the time are afraid of sounding loose/wanton/whatever or are just embarrased. So don't expect a lot of audible evidence. That's why the hand below her navel is so useful - you can feel what you can't hear. When you find something good, she'll probably gasp a little. Make sure it's a happy gasp, then find the gentlest way to repeat the same thing. Explore a little and see if you can get a bigger gasp.
7) sexual excitement correlates with lubrication. If you're doing the right things, she'll get damper. And when she's really interested, her scent will change (generally milder). Play around the damp areas with a moistened index finger. Remember-fingernails are bad. The perineum is often quite sensitive. Once you figure out what she likes fiddled with, it is probably time to introduce your tongue and lips. I've generally had good results with keeping the finger in the neighborhood and augmenting with the mouth.

when you really get her wound up (could be five minutes, could be 20), she'll get more lubricated and will get the female version of an erection (Yes, it really happens-there's erectile tissue beneath the labia that open up the entrance to the vagina). You'll feel more tension in her legs and abdominal muscles and her respiration will be shorter and faster. She'll probably start to perspire a little.
9) At this point, it's probably time for your finger to boldly go (gently, actually) where you hope other parts will be later. Angle things so that the nail isn't rubbing against anything. The tissue in there is as soft as the inside of your mouth, and doesn't like roughness any better. The ring around the opening is sensitive - explore it with the pad on your finger. If she has a hymen, you'd be wise to keep getting her as excited as possible up before you try to stretch it.
10) generally, the most sensitive part of the vagina is the area just below the pubic bone. Your finger will detect a different texture there. This is the "g spot," and isn't usually a spot as such, but more like an area of different tissue. Explore it with the pad of your finger. Once you find a motion she likes, you can start working with your tongue around the clitoris and hood. Again, gentle is the key - remember that the upper surface of your tongue is actually rather raspy.
11) if this is all going well, you'll soon have a new challenge. She'll probably start squriming so much that it's hard to keep finger and tongue where you want them. Ganbatte!
That might just be as much as can be conveyed in writing. The principles remain the same: go slowly, pay attention, be patient, and be gentle. If she's inexperienced and doesn't masturbate, you might be at this for quite some time before you manage to rock her world.
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