I want to address the specific challenge of painting folded fabric because it's a foundational skill for figure work and character illustration that gets less dedicated instruction than anatomy or perspective.

Fabric folds have a structural logic derived from gravity and from the points where the fabric is attached or constrained. Understanding the logic means you can construct any fold rather than copying a specific photograph.

The attachment-and-drape principle: fabric hangs from attachment points and falls toward the ground along the path of least resistance. The fold radiates from the attachment point. The more fabric there is between two attachment points, the more material excess there is, and the more folds form.

Weight categories: heavy fabrics (wool, denim) produce deep, wide folds with few creases. Light fabrics (silk, chiffon) produce many small folds with complex overlapping. Understanding the weight of the fabric tells you the character of its folds before you've drawn a line.