If the OP minds, I will be happy to delete this text and send it in a PM but here goes.
First, a disclaimer, I am absolutely not a professional photographer and I don't know anything substantive about studio shooting. My entire experience has been in natural light and so all my ideas come from that.
All that being said, here goes.
The idea about shadows is that you want the softest shadow reasonably possible. That will define the surface and yet not produce deep impenetrable shadows. It's pretty obvious that a small light source produces sharp edged shadows. The shadows from the sun are quite sharp and are softened at the edges only by some amount of diffraction and by the fact that sun does have some width and isn't a real point source.
What is desirable is much softer shadows with a long transition from the unshadowed part to the deepest shadow - hence the use of soft-boxes enclosing flashes or bouncing flashes off walls and ceilings; both of these diffuse the light and make the source effectively much larger.
Well how does one get soft light with the sun?
On slightly overcast days, the clouds diffuse the sun, making that soft transition that is so nice and so the shadows are soft-edged and not so dark. This is also found in open shade where some of the light is filtered through the trees and some of it is bounced in from the sun as reflections. Some people have set up studios in their garage where all the light is bounced off the driveway and thus it is directional but very soft.
What we get there is a large soft light source that models all the features and yet the shadows aren't too dark.
Of course you have to notice about color tint from the source.
Most important in any portraits, imo, that the eyes eyes be clear and sharp and that the eye sockets should not be dark holes under the brow. Of course there are exceptions to this but in general viewers want to see the eyes well.
Here are
some casual portraits that I've done. These aren't necessarily contest winners or even contest quality but they are dear to me and, as objectively as I can judge my own work, nice pictures.