Okay, this is going to sound fucking awful, but trust me.

Take the tip of any finger, pinky is best, and stick it against the tip of your tongue gently and start trying to make circles around it. As tight, and consistent, and perfect as possible.

Okay, got that? Awesome.

Now do it nonstop. Do it until your head spins a little and you feel a little crazy because the only muscle moving in your body is the stupid little one in your mouth. Do it until it is bordering on a zen practice and is becoming almost meditative. Throw some music on in the background and do something else to veil the passing of time somewhat.

Now once you have the one direction down, do the same thing the other way so your counterclockwise is as smooth as your clockwise.

You should be able to spin your tongue in perfect, rhythmic, concentric circles around your fingertip, for at least 20 straight minutes, with no lagging in pace. I am not kidding.

That is the single best advice I can give because I did it myself and have seen the difference from when I started to now. My current GF hadn't ever cum from oral prior to me and it was during the process of finding what makes her tick that we discovered she responds well to tight circular motion around her clit because it provides constant sensation, while still having spikes of intensity when you master the finer movements enough to make one or two of the semi circles making the circular movement a little sharper or broader.

At this point, I can seamlessly fade from an elliptical with soft long sides and sharp short sides, to a perfect circle that tightens and loosens, to an opposing circle, all the while going from providing a little suction, to not, and back again. The goal is being able to use my lips, tongue, and suction, completely independently of one another, within physical limitations.

It also gets interesting when you start doing shapes that mimic the circle but are actually just an illusion. Like using the right side of the tongue in an upward motion, sweeping it left and down, and upon getting to the tip of your tongue, smoothly sweeping the right side of the tongue upwards again. It more closely resembles an soft x really if you look purely at the lines of contact.

Oh, last thing, visualization is key. When you're in the zone, doing your perfect circles, maybe getting a little g spot stimulation with your one hand, throwing a little suction in now and again, don't forget to picture the shape your tongue is making in your mind. Clear everything but a black square of space where you imagine your tongue tracing over it. Really focus on tightening the stray movements that stagger the smoothness of your tongue. Consistency and constancy are two big factors with making women cum I find.

Anyways, this is what happens when I have good music on at 4am and no one to tell me I am going overboard on this comment.