Probably the best advice would be to just have fun, but I particularly like Dungeon World’s advice to “Play to find out what happens.”
This advice doesn’t necessarily to throw out any preparation, but instead be open to where the game goes and go with it. Some of the most fun games I’ve run have been ones which were almost entirely run on the fly. It’s exhilarating, but admittedly it can be exhausting, so you can’t do it all the time. But, when you do play to find out what happens, amazing things can happen.
It’s been a fun month with this year’s RPGaDay. I hope you’ve enjoyed it too!