Step 2: track the motion.

Clothes flow over the body like water. The folds on clothes are determined by kinetic force and gravity.

Poly is twisting at the waistline and the part of her shirt thats tucked in is pinned in place but her chest and shoulders have rotated to the left (our left) and pulled the fabric along with them. What results are sweeping lines from the shoulders to the tuck point.

Her right leg is forward which pulls the fabric tight over her upper leg and creates a fabric flow in the direction of motion.

Let's see how this works.