Cold tap, pocket handkerchief.

Same as my laptop screen/keyboard - I use a dab of Dawn (or whatever brand I currently use) and a moist very soft sponge and dry with an old teatowel.

Zeiss wipes.

Tap water and a bath towel.

I bought so many microfiber cloths that when one gets too dirty, it goes to workshop duty and I get a new one for glasses.

For cleaning lenses properly (which I do once a week or so), I tend to use lint-free tissue (Kimwipes) and a mixture of 85% petroleum ether & 15% pure isopropanol; both of which should be available at your local hardware store. Bonus is that this is also appropriate for scientific optics, like microscope/camera lenses & instrumentation components (mirrors, prisms etcs) - just don't rub them!