You can't imagine what it's going to be like, so don't worry about it - and try not to worry too much when the baby comes. You really aren't going to get it wrong and fail your child spectacularly. But with the first one you will learn as you go along - I recall the first time I took my DS out in his pram, he bounced around like a pea on a plate with every bump in the pavement as I hadn't thought of putting anything cosy under him and he only weighed 6 pounds...
Don't be freaked out by how competent other new mums seem to be. Chances are they have close friends/family who've given them tips. Watch, learn, copy if you like but don't feel like you're the only one who doesn't know what you're doing. No one does initially. Some people just shop more. 
I used to marvel at people with 8 million toys hanging off their pram and an immaculate nappy bag full of goodies, but the chances are their child was oblivious to it all anyway... But on that point, pack your nappy bag now. I have a Pacapod with lots of compartments and I literally couldn't work out what was supposed to go where when my DS was born. It's still in a right old state. Anything that comes with an instruction manual needs to be sorted out now. You will have no short-term memory or intellectual resources once the baby comes. Don't kid yourself about that. The sleep-deprivation really does make you thick.
Don't bother with cute outfits for you or the baby. Comfort is key for both of you! Getting back into your pre-maternity jeans is highly overrated. I have a friend who got pregnant again before she stopped wearing hers (about nine months after giving birth...) And don't worry, your tummy will shrink even if you never manage to do a sit-up. I still haven't, and my DS is nearly 14 months. Suck in your muscles when you're pushing the pram if you're bothered. I really wanted to do post-natal exercises but I never actually had time and I ended up not caring at all!
If you're having a winter baby, do try to make it outside in daylight even for ten minutes. Don't worry about the lovely summery things you can't do with them, like leaving them in the back garden to look at branches waving in the breeze... Get a pram suit for them, preferably a size too big as it's easier to wedge them into it, and go for a quick walk. I used to go to a coffee shop and have something to eat, which was usually lunch, by about 4pm... Dinner would happen some time after ten, often while I was feeding my DS. My DH fed me by hand a few times which was both funny and heartwarming. We ate random food for the first three months, mostly cold, as my DS seemed to wake up as soon as a plate hit the table.
Mostly, I lived on toast and cereal bars. The latter are great in the middle of the night. I lost my appetite from stress and shock as my DS was early and I couldn't get my head around it, so cereal bars were all I could stomach. I couldn't even eat chocolate... Eat lots, small amounts if you aren't in the mood for much, and bfing makes you both thirsty and ravenous so watch out for that. Chewing gum is also a lifesaver when you can't get to brush your teeth (like when holding a sleeping baby who won't stay asleep if you put him/her down).
My DS was a horrible sleeper and a long-drawn-out feeder. Get a feeding cushion so you don't have to hold them (assuming you're BFing - and even if you're not, some babies take hours to finish a bottle so make yourself comfortable). Get a steriliser and bottles even if you are planning to BF; we had to dash out to get them late one afternoon after the midwife visited and told us to top him up with formula. All breastpumps are hideous. Some people don't find expressing easy at first/at all. Don't feel you have to keep trying to pump instead of using formula. I fed my DS until he was over a year old, but the first few weeks it didn't go well and he was topped up. We gradually reduced his formula feeds and got back to just BFing - it can be done and don't let anyone tell you you're threatening your supply if you resort to a bottle in desperation. It is tricky to cut down on FF though, so if you can, stick to BF as much as possible. But learn to do it lying down when they're a bit bigger! BF is much less hassle than formula once you aren't exhausted and desperately stressed, so persevere if you can. The NCT helpline ladies are unbelievably lovely and always super-helpful if you need a boost. And the great Tiktok on the bfing thread here is a fount of knowledge.
We didn't have any visitors for the first week; we needed them! Don't be afraid to let grandparents come round if you need a hand or want to sort things out. They don't want entertaining; they just want to sit and stare at the baby, so you can go and sort your life out. I barely slept in the first week (which you can do because of the hormones; you feel like Superwoman but don't be fooled, you need rest.) Never got the hang of sleeping while the baby slept, but my DS settled him at night after I'd spent an hour or more feeding him as otherwise I would feed, settle, and get about 40 minutes' kip before it started again! It was great for him to be involved and it meant I wasn't totally shattered - just a bit shattered...
Lots of newborns won't sleep in a cot/moses basket; get a sling so they can snooze while you make yourself a cup of tea or eat or just go for a walk. And co-sleeping saved my life though I didn't think I'd like it and wasn't planning on it. The DS got the hang of sleeping alone in the end.
Get a dryer if you don't have one; you won't believe how much laundry you'll be doing. Buy a few sets of pyjamas that you can feed in. Buy sleep bras so you can wear breastpads during the night and avoid leaking everywhere.
Expect nothing of yourself - just look after your baby, look after yourself as best you can and know that things settle down before too long. The first bit is the hardest; it gets easier from here. And people do it again, so it must be worth it. 