Fabric drapery drawings are among the most important elements in your drawing skill set.
Fabrics are tricky to draw because of all the Folds and complicated shading.
I’m not sure if I can offer much advice beyond drawing what you see…..
But here are some things you can consider before starting :
1. Use various grades of pencil for the drawing : HB, 2B, 4B, 6B and 10B if necessary. For blending you may use blending stumps.
2. Start shading from the dark areas first. Feel free to use 6B in the darkest crevices,but use it sparingly. If your fabric is supposed to be darkly coloured, darken the whole picture, keeping only the highlights white.
3. Leave the directly illuminated parts with less contrast. Notice how the shiny stripes connect in arcs to points where there are no folds.
4. Finish the drawing by dragging your eraser along the shiny stripes to make them stand out even more.
Here, take a look at some more references: