What is the proper way to clean a focusing screen?
Last week I bought an EE-S screen in a shop. I go back and find a little scratch on it then I go back and ask for a new one.
That idiot take out the screen and use the finger to hold it and give it to me.
Then I tell him he made a fingerprint on it. And tried to use a lens cloth to rub it but I say it will scratch the screen...
And they have no more stock.

Instructions that come with the most delicate focusing screen the Intenscreen by Beattie indicate that one should clean it as follows:
Use a mild dishwashing liquid in a ratio of 1 drop to 1 cup of warm water. Dip an unscented tissue into the solution, squeeze out the excess and gently wipe the screen. Use a second tissue with water only to rinse and blot dry with a dry tissue. NEVER USE GLASS OR LENS CLEANERS ON INTENSCREEN.

I cann`t guarantee that it works with other focusing screens.

Cheers,
T

I agree with Toenis, washing up liquid with water works best on any glass, after I polish with a cloth that comes with my glasses, you can get this from any opticians.

The cloths are called "microfiber cloth" and should be available from most opticians.

Alternatively you can use wood free paper that comes with lens cleaning sets.

In all cases, only use the paper / cloth to remove the water, don't rub. (on the ee-s this would definitely destroy the fresnel structure).