Gather a few sweaters, cashmere is preferred for its long fibers, but other yarns or fibers will work also. I have used Merino wool, Lambswool, Silk, Alpaca, etc. Clean them (washing machine is fine even for wool, use cold water & regular soap. If it shrinks or felts, that will work to your advantage.) and line dry them.
Step 1: Cut into strips
Cut each sweater into strips. I like to start w/sleeves first. If you have enough time and patience, you can try to cut straight, following the knitting. Since you will be using fusible webbing along the seams later, this is not necessary, although it does look much neater at the end. Most of the time, the sleeve cuffs and neck cuff will not be practical for this project, however, if you save them, they can be made into other products.