Greetings.
I use the Meguiar's clay bar method. Very easy with beautiful results.
A recommendation I would also make would be utilizing a Mr. Clean Magic Eraser.
I use this little sponge with the Meguiar's quick detailing spray.
This little eraser is nothing short of amazing. It has proven to be very safe
and effective on my vehicle windows.
These are available @ Wally World and cost effective. Here's a link to their website.
Clean Walls and Erase Set-In Dirt with Mr. Clean Magic Eraser.