Brain Rules for Baby (by John Medina) to us. In all honesty, I wish I had started reading it prior to Baby L's birth; for creating an environment to optimize your child's brain development, I highly suggest that you read this book! There is so much good content that I can't really summarize it all, but suffice to say I am learning a lot and plan to practice doing the things the book recommends, especially praising effort and guiding imaginative play and practicing intentional empathy (plus not fighting in front of Baby L, and making up with Hubbs in front of her when we do).
Go read this book. Now!