You're leaving the hospital with your newborn baby, feeling either pretty proud of yourself or pretty shitty about yourself, and wondering what on earth you're going to do with this sweet, helpless little person that somehow came out of you. You get home and soon realize that you'll be attempting to nurse, changing diapers, attempting to nurse, changing diapers, attempting to nurse, changing diapers on a nonstop loop, spelled only by going to the bathroom to change your pad and looking at your partner saying "We have a baby!" with a mixture of wonder and fear.
When you're doing nothing but lactating and changing diapers, your partner has to pick up the slack by doing everything else involved in not only running a household, but changing your entire way of life. Plus fielding phone calls and dealing with a crying baby and crying mom (the hormones!). It's really hard.
You'll need help.
It's easy to think about how romantic the first few weeks after the baby's birth will be, when your cozy little family will be working things out. And it's true that it might be like that. Some people have a pretty smooth postpartum period. But it's also a possibility that you'll be either a little or a lot overwhelmed, the three of you, with odd sleeping schedules and engorgement and sore nipples and poop all over and dirty laundry and crying (all three of you) and friends demanding pictures and thank-you notes and it's-8-o'clock-what-are-we-having-for-dinner? and you're all just so tired. And it would be really helpful to have someone there who could fix you some food or take out the trash or even just smooth your hair and tell you you're doing a good job.
You need someone who will actually help you, not make you cook or make tea or have certain things on hand while s/he holds your baby and gets all the sighs and coos you should be getting. The only people who are allowed to come for more than an hour are people who understand they're there to help you, not just fawn over the baby.
It should be someone you feel comfortable being topless around, because learning to nurse is a full-time job, and you need to be able to let it all hang out literally while you're figuring out the logistics. More than a few women have had their breastfeeding relationships torpedoed by having too many visitors for too long that they couldn't nurse in front of. And don't even think of allowing anyone to come "help" if they're not committed to helping you do everything you can to establish breastfeeding successfully. You may not end up nursing, but if it's because someone else interfered with it in the first few weeks, you'll be resentful for a good long time. (For more on the first few weeks of nursing, read "Breastfeeding: What's the normal learning curve?".)
It should be someone who either has your same parenting style or has no preconceived parenting ideas or keeps her ideas completely to herself. You need support and validation, not someone undermining what you're doing.
You need someone who will let you do the parenting while you figure out your rhythm and routine, not someone who wants to jump in and "fix" things with the baby for you. You're the one who went through the long wait for a baby. You are the perfect mother for your child. No one else can do this better than you can.
You need someone who will take care of you while you take care of the baby. Someone who will do your laundry and wash your dishes, make sure you drink enough water, tell your partner s/he's doing a great job, and call the lactation consultant for you. Someone who will sympathize about hemorrhoids, and listen to you and not judge you when you whisper "I think I made a horrible mistake," and tell you that yes, the baby is clearly a genius because she recognizes your voice already.
You need someone that you can stand to be around for hours at a time during the most sensitive and confusing time of your life, when hormones are coursing through your body. Anyone who rubs you the wrong way after a few hours during normal times will make you want to stick a pencil through your eye during the first few weeks postpartum. (Which would be counterproductive anyway--you should stick a pencil through the other person's eye instead.) Stress is not going to help you take care of your baby, learn to nurse, or be able to catch some sleep, so don't invite people who stress you out into your house.
If this means that you can't let your MIL (or mother, or best friend) come stay with you for the first few weeks, decide that now and get your partner on board and get your story all ready. You can come up wth any number of excuses about why they can't come stay (hint: when in doubt, blame your pediatrician), but don't let anyone guilt you into inviting stress and discord into your house.
Let me say this one more time:
You cannot allow someone to stay with you if they're going to stress you out.
The newborn period is the time for you not only to bond with your baby, but also to develop your confidence as a mother. If you don't have any support, or you have someone telling you you're doing things the wrong way, you're going to feel like a really shitty mother. If you start out feeling like a shitty mother (instead of just a slightly inadequate and unorganized mother, as
most many of us do), it's hard to climb out of that hole, especially if you still have no support or the wrong support.
If you don't have a person who can come help you for a few weeks who won't stress you out, consider hiring professional help. There are two kinds of professionals you can hire: baby nurses and postpartum doulas.
If given the choice, I'd choose a postpartum doula over a baby nurse for a lot of reasons. The main reason is the focus of care they give. A baby nuse is there to take care of the baby, not to take care of you. This means that you'll be fixing your own food and doing the laundry while she's holding the baby. She'll be bottle-feeding the baby pumped milk at night while you
sleep pump because your breasts are so full you can't sleep doze lightly hoping the baby won't cry. For some women a baby nurse is a big help, but I've heard too many stories of women whose confidence was undermined by bossy baby nurses (who aren't actually RNs or LPNs, even, just women with varying experience who sign up with an agency) who ignored the mother and took over the baby. You hire a baby nurse by the day (for a 12-hour or 24-hour shift, usually).
A postpartum doula, on the other hand, comes to take care of the family while the parents take care of the baby. There's a great description of the kinds of things postpartum doulas do on this site. Full disclosure: One of my friends is a postpartum doula. The things she does for a client are cook big meals (including some to freeze), cleaning bathrooms and kitchens and floors, doing laundry, addressing birth announcements, helping with simple breastfeeding problems (like positioning problems) and helping you decide if it's serious enough to call the lactation consultant about or if you can wait for the breastfeeding support group in a few days, holding the baby while you nap or take a shower, playing with older children, fielding phone calls from family and friends, helping look up odd things in the baby book, dialing the pediatrician, and telling you you're doing a great job. A big thing she focuses on is helping you set up your routines, so you can be self-sufficient once she's gone.
A postpartum doula is likely to have gone through a certification process, which includes training in breastfeeding support, recognizing the signs of PPD (not just normal hormonal moodiness), understanding newborn behavior, and normal stages of emotions for the mother and her partner. You hire a post-partum doula for a set of hours (usually 15 to start), and she works those in 3-hour chunks (usually a 3-hour shift every other day, or as needed).
If you are interested in having a postpartum doula but can't afford one, call up your local La Leche League leader and explain the situation. She may know of a doula-in-training who needs to work at a discount while she's getting certified.
Whether you end up with your mother, a postpartum doula, a friend, or even your unmarried little brother (who can order in food for you, do the laundry, and load photos of the baby onto your Flickr account), make sure you choose someone who's going to be kind to you and your partner while you learn your baby and your new lives. You can absolutely come back from a crappy first few weeks, but it'll be much easier to stay on an even keel if you're already feeling good about yourself and your skills by the time the 3-week growth spurt hits.