Simply place the self-tapping screw on the outside line guide of the rail and screw into the gutter. Use three screws per five-foot piece – secure one screw in the middle and one on either end of each piece of gutter guard. The gutter guard will be fully secure when the self-tapping screws are installed through the rail and the top of the gutter.  Many installers prefer starting from the inside miter, outside miter or at end of the gutter.