My mother taught this to me. Trim the loose threads and turn under a small seam allowance on the hole. On the back side place the patch under the hole and pin or baste in place. By hand stitch the patch in place using an invisable stitch. It is kind of like reverse applique. I know, this is clear as mud. It really does work well especially if you can match the color of the jeans and the patch. When I grew up on a farm jeans were for working or playing outside. Patching made them last longer.