Another go at understanding how this stuff works. There’s a whole world in a scrap of fabric!
Painting drapery is an advanced skill but not impossible with care and attention to breaking the problem down into simple steps. The same as any other painting – drawing the shapes and simplifying the values.
Drawing is just making shapes. Big shapes first. Small shapes later. Limit the values of those shapes to just three to begin with – light, mid and dark. Squint to see them! Mine have been broken down a little more as the painting progressed but if you squint you will see that there are really only three at the finish.