It's not easy, that's for sure. I've always heard that you should take them as early as possible, and this seems to be true (though all babies are different.) The first two days I shot, where she was still under a week old, went pretty good. She stayed pretty sleepy for the most part and I was able to pose her a bit without disturbing her too much. But it seemed as soon as she entered her second week, this changed completely. No more posing her...heck, all I did was lay her down, asleep, on the blanket and she would instantly wake up crying as if she were being tortured. So, though I would have liked to have kept taking more and more photos of her, she wasn't having it, and I had to call it quits.
And speaking of posing...posing newborns is not an easy task. Even when they're in a deep sleep and will let you pose them, it's hard getting them into the pose. I kept trying to put her into that typical newborn pose where the head is resting on folded arms, but could not seem to manage it! Her arms just didn't want to go that way, and even if I did get them into position, she would quickly slide out of it. So in the end, I let her do her own thing, and just made small adjustments that wouldn't disturb her much.
Another fun of part of newborn photography that you might not think about...they can be pretty messy. Most newborns are shot naked and diaper free. And if you've ever had a baby, you know that they go to the bathroom a lot. So its not a question of if they're going to potty on the cute fluffy blanket you're using as a backdrop...it's when. The idea is to just snap as many photos as you can before they do make a mess.
Wraps are a great idea. They solve the mess problem, because you can keep their diaper on and it'll be hidden. They also solve the posing problem. You don't really have to worry to much about their posing when their in a wrap.