I've done a few "at-home" modifications to my car over the years, and this one is one of my favorites (and also the easiest!)
Remove your taillights from the vehicle using screwdrivers or sockets if necessary. The lights usually just twist to one side and pull out. Clean them with wax and grease remover, and let air dry.
Carefully tape off any portion you don't want tinted, in my case, I kept the reverse and turn signals as they were.
Step 1: Homemade Tailight Tinting
Wait ten minutes between coats, and apply as directed.
Step 2: Homemade Tailight Tinting
Simply re-install them on the vehicle, make sure the bulbs still light up, and there you go! I advise to apply a light coat of wax (same stuff that you'd use on the car itself) to keep contaminants from eating at the clear coat over time, but otherwise, it's easy as pie.