Face shapes can be as simple or as complicated as you want them to be. (Some people think the concept is outdated altogether and prefer to think in Big Picture terms of “types.”) If you want to reduce them all the way to their simplest elements, you could think of the basic shapes as a triangle, square, and circle, with all other shapes being a modification of these. (Place cursor over images for a fuller explanation.)
The real trick to understanding complex face shapes, I believe, is to sort out their combination of shapes. An oval or oblong face, for instance, morphs into a diamond if you narrow the forehead and jaw and then stretch the cheekbones out. You could think about it as two triangles, one regular and the other inverted, on top of each other, intersecting at the cheekbones. Some round or squarish faces become “ovalized” at first glance by the addition of a longer chin and jaw that appears pasted on at the bottom. I’ve seen face and jaw treated as one oval, but also as two separate things. Either way, it’s about understanding the effect as a whole.
Additionally, a profile can change the vibe of the face. For instance, in profile a rounded forehead will add a curved line, and a jutting chin or nose can add an angle to an otherwise soft face shape. These can change the apparent softness or sharpness of a face, even adding a geometric element if they are pronounced enough. You can probably get an idea from the complexity of elements how it’s possible to have a square or rectangle face, and yet for the “corners” to be very soft instead of sharp. Or that someone with a round or oval face can end up with pretty sculpted features instead of soft ones.
Where there is notable divergence between the lines of the face and the body, some believe the optimal result comes from dressing 50/50 for the face and the body. I have seen it demonstrated to some satisfaction where two women had identical body shapes and proportions but completely different faces. However, I’ve lately had a different take on it. As I think back to that demonstration, the one woman had a face type that matched the body type and the other did not. I am more persuaded now to think in terms of macro-outlines — that is, the overall outline of the head + face and skull. I think divergences are a matter of proportional percentages. If the divergence involves the skull + outline of the face, you have to think of it as modifying the body itself. If the divergence is mainly in part of the face shape, good possibility it’s a strong modifier but doesn’t change the macro-outline. If the divergence is only in the chin, cheekbones, or other features like nose, mouth, or eyes, then it’s a modifier of details.
The spacing between facial features is important, too. The spacing of prints, jewelry, and other accessories like button or embroidery, for instance, should mirror the spacing between facial features. Tighter facial features indicate a compatibility with tighter details. Faces with more spaciousness generally require more “air.”
I hope you see this expanded idea of how lines and shapes + space work together. You have to sort through a lot of generalized information where you read what’s available in style consulting literature, then analyze your own specifics to plug into your style formula.