Ideally you would use some type of mechanical fastener (screws, spring clip, etc.) along with thermal grease to fasten the LED to the heat sink, but that is not always practical. So most designers use double sided thermal tape which is quick and simple to use as shown in the video below.
We offer a selection of pre-cut, thermally conductive, electrically insulative adhesive pads for our pre-mounted Luxeon Rebel LEDs and other LED configurations.