On writing a first chapter:
"Readers don’t need to know how our characters got to the point they’re at. Throw our characters into the story and for the first chapter pretend the reader already knows as much as we do."
~ Jody Hedlund in her blog post Potential First Chapter Problems
I knew this is something we should aim for in a first chapter, and I've striven not to weigh down my first chapters with too much set up, but I've never heard the idea phrased quite this way before, pretend the reader already knows as much as we do. That clicked it into focus for me in a far more conscious way, so I can be more deliberate about it in future.
Check out Jody's post for the rest of her tips on first chapters.