I usually have my concepts well planned before the session. However, when the poses aren't strenuous, I can play a little while shooting. If I see something that strikes me while shooting, I can change the angle, lighting, pose, etc. Or my subject might improvise a little.
With these looks, we took a more conservative approach and stuck to my original plans, keeping adjustments to a minimum.
I also wanted to incorporate the cholla skeletons in a fine art portrait. I like having elements of nature blended with the human form. However, when I do this kind of look, I also like the extreme, awkward, artistic poses that accentuate form.