Fabric Preparation~

Whether you are getting your fabric from thrift shops or quilt shops you should prewash all materials before putting it all together with needle and thread.

Some fabrics shrink more than others. Wool for example can shrink up to 40 percent. Some people choose to not prewash wool and they just rather keep it away from the dryer and that is up to you. (Just remember your wool sweater that shrunk to baby size after being thrown in the dryer)

Wool aside, most fabrics such as hemp and cotton need to be prewashed before any Dyeing or sewing takes place. This is simple~ give the fabric as much stress that it will ever possibley go through. This usually means wash on hot in the washing machine and dry on hot in the dryer. Be sure to iron the fabrics before construction. I use equal parts Baking soda, shaved (natural) soap, and Borax about 2 tablespoons in the wash or a natural wash bought from the store.
Sometimes water alone is good.

Also washing trims is a good idea, but it can be very tricky in the dryer. It can easily be put into a small drawstring bag and thrown in the wash. This goes for any cotton or natural fiber trims.