Wetsand with progressive grits (320 / 400 / 600 / 1000 - start with 600 if it's not too bad to begin with)
3M Rubbing Compound w/electric buffer
3M Finesse-It II polishing compound w/electric buffer
Wax
It's a lot of elbow grease, but it'll put a shine on it like it just came out of the mold.