The Rule of Thirds is a classic rule for composition. In the shortest form, it says you should place things in your frame where they intersect the lines dividing the frame into thirds. Using this kind of goes back to getting your subject out of the center of the frame. The rule of thirds gives us a guide to where to put them.
You should put your vertical subjects along the line between the center third and the side third. Doesn’t matter if it is on the left or the right side. It should be on the “third” line.
If your model fills the frame, then put her eyes on this third line. If you can put them on both the vertical and horizontal third line.
For example in this image of Amanda her face is right on that line. Yes, there is a lot of empty space in the image, but your eye goes right to her. The image is dramatic and it has an artistic feel to it.
Once again we can use the nine square grid on our camera to find this point. You don’t have to be super strict about getting it right on the cross point, but pay attention and use it well.