So what if you character is wearing a skirt that is blowing in the wind or some other force acted upon it? You look at the direction of the force that is acting against the fabric and define the flow of the cloth. In this case, I drew the basis squiggly lines before I added the inner detailing as well as the upper. Once I did that, I connected the lines to the base of the skirt which climbs up the thighs. To create depth to your drawings, as well as foreshadowing, use brief sketched lines in a set angle. This will add 'POP' to your drawings.