Great question!
As a team, I think we learnt how to find a middle ground for all our ideas, speeding up the decision-making process. This was very important and led to unexpected results of our creativity mixed together!
Also, how not to get too attached to your own idea of how something in the game should be -- sometimes it's just better to let go!
I believe the biggest one was that a limited time span for developing a game is a parameter and not a limit. This totally put us in a productive mindset and cut off all the frustrating "if only". We just started writing down all the ideas we had as extras and now that the jam is over we have plenty to work on!
We somehow found a compromise with that also by placing hints in the game suggesting that there's more to it. So far it looks you kind people who tried it found many of them, and that's awesome!