When I've done it, I pin in the ditch on the front, parallel to edge of the binding, very close together. When you're pinning, make sure you have a little bit between the pin and the fold of the binding to the outside of the pin on the back. That way when you are stitching, the stitch line is on the binding. I use my walking foot, go very slowly, and stitch in the ditch on the front. You may have to go back and restitch a little, but not too much.