I've got a few years experience with Pathfinder 1e (player & GM both) and some playing experience with D&D 5e and I recently ordered the Basic Hero's Handbook, Rogue's Gallery, and GM Kit for M&M 3e. I'm going to run a one-shot or two, possibly spinning it into a short campaign, for some friends. Some of them play PF, some play 5e, one plays Call of Cthulhu as well as PF, none of us have played a superhero system before.

I've read the FAQs and some stories on this subreddit. What should I know going in, and is there anything I should warn my players about that might not be in those? What would you say to yourself when you were just starting M&M?