What's the best explanation you've heard for permissible assumptions on the LSAT?

Hi all. I'm an LSAT instructor perfecting my craft, and I'm looking for the best, clearest and most helpful explanation you've heard for what assumptions one can make on the LSAT.

For instance, I've heard of people using the "man on the street" test, meaning that if it's something a random man on the street would know, then it's okay to use that assumption for a question. But I'm concerned that that opens the door to students confusing themselves and overthinking what a random man on the street would know. Basically, I want the most idiot-proof explanation you've got!