From The Gluten-free Gourmet Cooks Fast and Healthy by Bette Hagman

2 parts white rice flour
2/3 part potato starch flour
1/3 part tapioca flour

Make a large batch of this flour mixture to keep in a canister for ready use when flour is needed in a recipe. In a pinch, quinoa flour works well on its own. Try white or brown rice flours, garbanzo flour, and many others if you want to experiment and see what works best for you.