I have a book on this (that I can't locate right now
). Basically, you cut 2 pieces of fabric in an oversize square or rectangle of the piece you are aiming for, stack them, both right side up, cut a gentle curve with a rotary cutter, then swap the 2 fabrics, sew, and trim down to your target patch size. You get 2 patches. I'll continue to look for that book!
ETA: I can't find my copy, but this is the book:
http://www.amazon.com/Cutting-Curves...s=curved+quilt