I wish I'd known that not all babies like to be wrapped - I may have been able to get more sleep in hospital if I'd twigged earlier that it was my wrapping him that made him cry, not my putting him down...
I wish I'd slapped the night-shift midcow when it first occurred to me that it would be well-deserved.
I wish I'd insisted that they help me co-sleep safely at the beginning so that I didn't end up so sleep-deprived that it was no longer a safe option anyway.