If you want to pleasure your woman regularly with oral sex, you are already in the good track; this article will give you some advice on how to make sure you are making the right moves.
One thing women tend to forget is that as a guy you also become really excited while using your tongue down there: the idea of getting her off can be so hot it literally causes you to melt with lust. And just for this same reason, things can get tricky… the sensuality of the whole business can mislead you into thinking that she must be certainly having a good time too. Don't get this wrong, she probably is enjoying it in many levels (the mere bond of intimacy means a lot to her), but a couple little changes can be the difference for her between just good sensations and reaching explosive orgasms.
Tell her you really enjoy it
This first step is basic: not only she will feel more aroused by the thought that pleasure is flowing both ways, but she might find it easier to be expressive about what she feels with every caress if she knows you want in your own interest to make it as great as possible for her. What is more important, a channel of “sexual” communication may open between the two of you, a channel that will work to make you a better lover in many ways (including, yes, the ability to express what you like for yourself).
Convince her to move you along
Once you have managed to convey her the conviction that you want to do the best job with your tongue because it is her pleasure that pleases you, it's easier to make her understand that she won't be hurting your feelings if she gives you a couple of hints to improve your moves down her. You still need to sort out how to set up this guidance from her part without killing the romance and the excitement in the process, but the crucial stage will be cleared: she now knows it's a good thing to tell.
That's actually the term that describes the opposite of what this is meant to be like. Yes, you need to learn what she likes the most, but you shouldn't do it through constant interruptions of stimulation to voice out loud your questions. Much rather, you should figure out a system to communicate subtly the moments when pleasure is at a high peak and those moments when things are falling backwards. For instance, she could get herself in a position from which she can caress your head, and agree that she will be massaging your ear lobe whenever things are running fine, and rubbing your cheek when something needs to be changed, and then of course use intermediate signals to express if changes are going the right way.
Another option, if you both think your movements are already satisfactory, is learning to tell how much pressure she wants to receive at each point and on each part of her vulva. To manage this, you could set up a code of proximity: she can grab the back of your head gently to pull you closer when you are going over an area where she wants to receive more or faster stimulation, and keeping you at the right distance when you are crossing a spot that's too delicate for the current rhythm.
These hints are merely a beginning path in the extremely exciting discovery of oral sex in the company of your partner. So leave always a room for improvement, have fun and keep on learning!