hehehe....i have just the thing that u my fren...
(this is for e21 and e30,others..dunno how...hehe) :
things u'll need :
1.some sand(act as a sandpaper)
2.carwash liquid/any washing liquid will do
3.glass cleaner
4.autosol(for the exterior part of the glass)
step by step guide(interior of the glass) :
1. remove the bulbs n wiring from the headlamps
2. clean the headlamps with water
3. put in some sand and the carwash liquid
4. hold the headlamp on your palm and shake it!!!...haha...but dont be too rough or not the sand will damage the chrome part that reflects the light.
5. when u're done with it,clean with water throughly
6. clean it with glass cleaner(i use my RAIN X cos i dont use it that often on my car...hehe...if dun want to use oso can)
7. when finished,put it upside down(glass up,the base down-to let the excess water come out)
8. then put it in a normal position(the glass and base on same level)
9. leave to dry
step by step guide(exterior of the glass) :
1. when the headlamps are dried inside and out, put some autosol on the exterior and rub it to remove some minor scratches.
2. clean the excess
3. clean the exterior glass with water n glass cleaner for final touches(to make it clear)
there u go...haha...
btw,dont put on the wiring n the bulb back if the interior is not dry...leave it to dry fully,inside and outside...
*take note,this is just my experience,if u guys hesitate to do it,dont do it...hehe
cheers!!!