I consider myself pretty good at this. If I have a smeary, nasty windscreen, I'll try a detergent (Dawn) first. I use cotton terry towels.

Try Clay bar/instant detailer-just like on the paint.

Meguiar's Ultimate Compound-this has done wonders for me!


As a last resort: solvent.

Always be careful.

Turpentine removes pine sap, a usual culprit. I've used methanol and even acetone. Like I said: be careful. It WILL muck up a paint job in a heartbeat.