After you buy that nifty riffled gold pan, it needs to be "broke in." You can do this with some 60-grit sandpaper.
Begin by moving the sandpaper in a circular motion, starting in the middle of the bottom and working to the outer edge. If you're in the field and don't have sand paper, put some small gravel in the bottom of the pan with a little water and, using the palm of your hand, move it in a circular motion.
When you use the pan, rocks are going to scratch up the bottom, but this way you can give it a head start. Now, the flour gold will be more easily recovered as it catches in the scratches.