Re: how to paint wrinkles in clothing and scarfs?
I was taught to paint or draw drapery like any other surface. You divide it y lights and shadows just as though it were a face, flower, or any other surface you might like to draw. There are a few things to look at:
What is making the cloth wrinkle?
Is anything pushing or pulling, or in what direction?
What are the major forms?
How is the light hitting it?
So, If you are having trouble with this. I suggest using some cloth and actually draping it in various ways and then live drawing it, or snap a few photos, and draw the various folds. As you get to know cloth better. You can also use photos from fashion magazines where folds and wrinkes will e more subtle-- and just draw until you get to know the subject.
I used to love Salvidore Dali because of the sharp focus he put on napkins and cloth in his paintings. He is a good artist to study for cloth folds.