Fabric that has a pattern such as stripes or other prints can be challenging. The best way to approach it is to ignore the pattern initially, and just draw/paint the basic forms of the folds in the appropriate values. For example, the cloth above is a white cloth with blue stripes. I began by blocking in the dark and light values of the cloth in burnt umber as an underpainting, I did not include the detail of the stripes, I focused on the shape of the major folds and their corresponding values. On top of the value study / underpainting, I began working in color. For the shadow areas of the cloth, I chose a yellow ochre, light lavendar and violet blue combination (NuPastels). For the light areas, I used a creamy white. On the background, I added additional yellow ochre. Once I had the white fabric defined with shadows on the folds, I added in the stripes, following the contours of the folds. In the shadow areas, there is less contrast and therefore the pattern is more subdued, in the areas that are fully lit, the reverse is true and the pattern is very distinct. When working with patterns, it is generally more effective to imply them rather than to try and capture every nuance with miniscule detail, otherwise they may become distracting and take away from the overall strength/spontaneity of the drawing.