If you've ever installed a new headlight bulb only to have it blow up in a matter of days or even minutes, then you already know the importance of the proper installation procedure.
As we all know, headlight bulbs get extremely hot and if you touch the glass, the grease on your fingers will cause the glass to heat unevenly and burst. No matter how clean your hands are, if you touch the glass, wipe if off with a clean paper towel and some alcohol.