If you are working on velvet, courdory, chiffon, organza, crepe, organdy, and other lightweight fabrics hoop them gently to avoid marks. The simplest way to protect the fabric is to place a buffer between it and the hoop. This buffer can be fabric, backing, or even tissue paper.
Some reccommend you wrap the inner ring of your hoops for any embroidery on delicate fabrics. This will avoid snagging the goods, stops the fabric slipping and will cushion the fabric, avoiding a contact shine or deeper hoop impression. You can use bias binding or any soft gauze or tape for this.
Alternatively, it is even better if you can avoid hooping the fabrics at all.
Another option is to use a sticky backing. You place this in a large hoop and peel off the paper backing exposing the sticky side. Position your piece of fabric and press it onto the exposed area of the carrier.
Another alternative backing is a wash-away stabilizer. To use this technique, hoop a piece of water-soluble topping both under and over the area to be stitched. When the project is completed, simply remove the topping and backing by rinsing the fabric.