Honestly, simply that they should be prepared for the hardest 1-2 months they've likely ever had. I don't say that to be dramatic - it would have made a big difference to Vickie and myself if we had been similarly, and seriously, counseled. Yes, we had heard it as a throw-away description lots of times, and so treated it as such. Had someone gone into some details with us, we would have been better emotionally prepared for the challenge, and not doubted ourselves as much, which frankly made it more difficult.
In that vein, your friend should expect:
The baby will need to be fed every 2-3 hours. You _must_ sleep in between feedings whenever you can. This is all the more necessary as you will often have to change diapers, feed yourself, clean etc etc between many of those feedings. Get to sleep _whenever_ the opportunity presents itself.
The baby can (and likely will) lose weight in their first week of life as they learn to eat. This happened with Luke, and it was very painful and nerve-wracking for us. Keep at the feedings, and consult your pediatrician to keep your nerves steady. They're used to nervous first parents.
Beware Titler. that's what Valerie and I took to calling the "leche league" breast-feeding nazis. Don't know if the mother is planning to breastfeed. If she is, she should know it's a real challenge at first - a wholly new skill for both mother and newborn that takes practice; combine that with the baby's likely initial weight loss, and difficulties with feeding can be very demoralizing. We had a number of breakdowns over this. What you need then is emotional support, and if necessary, formula supplementation (though not with a bottle until a few weeks in, as a rubber nipple too early can confuse the baby, and then they won't take the breast). Unfortunately lactaction consultation attracts a _lot_ of rigid ideologues, for whom the answer to everything, including global warming and the Iraq insurgency, is that formula is unacceptable no matter what, that the problem is that "the baby's latch on the breast must not be right", and that it's somehow your fault. Seriously. If you need help with breastfeeding, talk to your pediatrician, get a _number_ of references to lactation consultants, and screen as many as necessary to find one with a compassionate and _flexible_ approach.
Prepare everything beforehand. Get all the materials you'll need for the first 1-2 months now. Crib, outfits, diaper supply, bottles, frozen TV meals, menus, the works. You want to make everything as easy as possible for those first challenging 1-2 months.
Daddy - Mom's going to need to recover for some time, especially as she's having a caesarian. You've got to step up and handle most everything outside feeding until she's mobile again. Suck it up until you can split the work evenly again - which even then won't be a big change at first, because feeding is a very, very big time commitment. Every 2-3 hours, each feeding can take 20 minutes or more (in our case, we had lots of feeding difficulties, and it could take over an hour to get enough food in Luke), you do the math.
Lastly - and this one I feel is the most-kept secret about your first kid: there will be lots of times when you have dark feelings and even dark thoughts in the first 3 months. Everyone (especially grandparents) always coos and raves about how wonderful it is to have a child, but bear in mind they're delirious about getting a new baby in their lives without the workload. This is definitely what Vickie and I were most unprepared for, and it can make you doubt yourself and feel like a very bad person. DON'T. It's perfectly normal. Consider:
The baby will not reward you with interaction - not even a hint of a smile - until about the 2nd or 3rd month. It's literally just a food tube that eats, pees and poos. On top of that, it screams - loudly - when it needs something. Mind you, what that something is will occasionally take some time to deduce, during which the screaming will not stop. You can't ask it what it needs, you can't ask it to stop.
Now add on top of that prolonged and intense sleep deprivation - the worst you've ever had - the anxiety over being a 'good' parent, and the near-total isolation from your normal life routine that makes you feel like you've given up everything for a demanding small mass of flesh that barely looks human and just won't stop screaming. Yes, that's written with some dramatic license, but it's what will go through your head occasionally.
To really drive the point home: at the hospital it was required before discharge that we watch a video about shaken-baby syndrome. That's the irreperable brain damage that a baby can suffer if shaken with any vigor. Our reaction at the time was: "My God, what awful people. how could someone do that? To your own child?".
Let me just say that the hospital required the video for good reason, and that after the first 2 months, our tone was different. I proudly say I'm a doting father who adores his boy, whose protection is paramount to me. But, as the video wisely counseled, there were times I had to walk away from the crib - just _walk_ away - and hit the wall or my chest or sigh or do whatever I had to do to take a pause, a break, to calm myself down, and so return to Luke calm and attentive to his needs. I don't think Valerie and I would ever shake him, but we understand why it happens - we _know_ the feelings that precipitate it. They're normal. You haven't slept more than 1-2 hour naps in a couple of weeks, seen anything of your heretofore "normal" life, done nearly anything for yourself, eaten take-out and frozen meals for weeks, and after changing a diaper and trying a feeding the baby still hasn't stopped their shrill, skull-drilling scream. It's _normal_ to sometimes get very, very upset, even angry, or doubt your own sanity. It's normal. Just walk away and come back after a few minutes to yourself to calm down.
And now, after that, some encouragement. It gets a ***lot*** better after the 2nd-3rd month. The baby eats less frequently. He _might_ start sleeping through the night. The frequency of poos, initially 5-6 times a day, dwindles to once a day, or even every 2-3 days (the pees keep a-comin).
And most wonderfully - your baby smiles. He magically transforms from a eat-poo-pee tube into a tiny person you can't get enough of. He smiles - for you! There's nothing better than walking into his room first thing in the morning, and he always smiles just because he's so excited to see his parents. And it only gets better from there (turning over, laughing, grabbing your face). The first 2-3 months will be a gauntlet, but they're really, really worth what's on the other side.