I consider the face to be the life of any miniature, most importantly, the eyes. If the eyes look bad then the entire miniature will look bad, no matter how good the paint job. This tutorial shows how I paint the eyes on my figures.
To start the eyes, I do a base coat of skin over all the skin areas on the miniature. There is no need to worry about excess skin tone over the eyes if you are sloppy.
I then block in the eyes with white, again it doesn't have to be perfectly neat at this stage and going larger is easier to correct than making the eyes too small.
Next I add in the eye color, in this case, a nice vibrant shade of green. If the green is too much it's very easy to correct it by re-adding white at this stage.
The pupil and lining of the eyes is next. I fix the eyes to the final size at the time I line it. Anything outside the lined area gets touched up later with the base flesh color. For this figure I used a gray rather than a pure black to line the eyes. Pure black can often give the miniature a more pronounced set of eyes than is desirable. I've also used skin shadow tones or brown to line my eyes, if I feel the miniature needs a color other than gray.
I correct as needed at this stage. When I am happy with the eyes, I add a white "hot spot" to give them extra life and the gaze further direction.
If the lining is too dark at the top of the eyes or uneven at any point, I don't worry about it at this stage. It gets corrected when I add eyeshadow and blend the skintones to finish the rest of the face.
It is important to note that eyes take a lot of practice. Acrylic is also a very forgiving medium. As long as your paint is thin, you can paint over or correct an area many times.