prepare for labour mentally - I dod this but didn't think at all about stitches afterwards. my labour was easy, my stitches not so.
dont buy loads of kit cos 'you won't possibly be able to live without it'. buy it as you need it.
sleepsuits - get ones that fasten down the front with poppers or zips. over the head ones are a pita, as are buttons.
be prepared for every hp you come across to have a different opinion on things. ie. ds had sore bum during antibiotics. iwas putting sudocream on it onky to be told my my afternoon mw to use bepanthan. she brought a tube from neo so started to use it, onky to be told by evening mw that sudocream is better. grrr.
believe in your own opinions and do things your way. it took me a good few weeks to realise that noone was going to take my baby off me for letting him sleep on his tummy (only way he'll sleep), or how I make his feed up. They're guidelines there to help, not law.
picture how you think the first few months will be! now erase it, it won't be like that at all! 
forget the housework in those early weeks. look after baby and yourself and enjoy him/her. housework will wait.
my ds is a challenging little mite - he has suffered from reflux, colic etc and has really struggled adjusting to the outside world (still is). I would get myself all upset that I didn't have a contented little baby that I could walk out in the pram like a proud new mummy. its been hard work and I dont mind admitting it. ask for help if you need it and accept help if it's offered.
try to enjoy every single day cos you won't get that day again.