As someone with a 19wk baby, I'm sharing some I received, some I've figured out, and some I'd wished someone told me! These are in those first few months afterwards
1 - You do not have to be super parents - if the house is untidy, but the baby is fed, changed and happy - so what? Any guest coming unannounced (or announced for that matter) knows you have a small baby, they won't mind.
2 - Babies cry for various reasons. If you've checked everything - too hot, too cold, wet diaper, hungry, in pain...and they are still wailing - it is ok to put them down some where safe, and walk away for a few minutes to get some space and get your head back in the game
3 - You know your child best - if they are sick, and you feel like the Dr is missing something - get them checked again. Doc's are human too.
4 - Breastfeeding ISN'T easy for everyone - for some people it's hard, it does hurt, and it doesn't work out like you wanted it to. Ignore what other people think and do what is right for your baby and you - formula these days is very good. Expressing is good also - but can do your head in if exclusively expressing (like I was). Don't judge others if you find it easy, but don't feel stink on yourself if you struggle or choose to switch.
5 - "Behind every great child is a mother/parent who is thinking they've screwed it all up."