If your automobile's headlights are discoloured or fogged-out, wash and dry them thoroughly and polish them with Brasso. I tried this out on my car and it worked wonders. I know some car detailing joints who will charge approximately Rs. 3k per headlight for this closely guarded secret. Now you know better.
Here's the fine print; it is always prudent to try it out on a little area of the headlight - just in case for some reason your headlights react differently to this stuff. And of course, try it at your own risk :-)