If you print a lot of text that doesn't fit on the screen, it scrolls off the top before you get a chance to read it. Most adventure interpreters handle this automatically and insert a "[More]" or "Press any key" or something similar when the screen is full. Adventuron apparently doesn't have this. Given that an Adventuron game can be played on lots of different devices, from web browsers with any window size to mobile devices, how do I know where to put a manual :press_any_key; instruction? Or is there some other setting to handle this?

Best to use : stagger instead of print for large blocks of text. It will insert a press_any_key between paragraphs. 

The pause on screen full is planned for a later release of adventuron, but the IO layer currently doesn't have a nice way to make it work on all devices yet. Sorry about that.

For room descriptions that are particularly large, you can use the is_mobile() function to display less text if you want on mobile explicitly. Desktop will generally speaking display the exact same amount of text no matter the screen resolution of the particular player.