Is it rough to the touch? If you can feel it start with a clay bar, preferably a blue one (Clay Magic is the main blue one you'll find in stores, the white Meguiars and yellow Mothers ones suck). If you can't feel it or after the caly bar hit it with a compound. You can do it one of two ways, either use a paint compound, which will probably take it all out in one hit but you might get some light marring that you'll need to hit it with a plastic polish or a cleaner wax and then finally apply a normal coat of wax over it, or you can use a plastic polish, this is probably going to take several applications by hand to get it to a finish you're satisfied with. I suggest taking the lens out, it's not much work just the rear panel in the trunk, pull the tail lights using the 4-6 plastic wing nuts on them, and then 4 nuts on the center section. Do the tail lights and the center section at the same time so the all look equally good.
Also, make sure you tape off the emblem, especially if it's original. The gold will come off with the lightest bit of compound rubbing on it, use painters tape (blue) to cover up the area.