I would go through the clothes and sort into piles of similar fabric content. Ideally cotton or cotton blend are easier to work with. That being said, you can make a quilt with other fabric they just have to be treated a little differently. If the fabrics are thick, pick a large design and use larger seams. Crazy quilts were made with silks, velvet, corduroy etc. There are some great blue jean quilt on quiltingboard.