Newborn babies have a tendency to unintentionally flail their arms about, which can agitate them, which can cause them to flail further, which can agitate them further, and so on.
The easiest way to calm them down is to swaddle them. If, like me 10 days ago, you're wondering what the hell that means, think of it like this: wrap them up like a burrito. With the baby's arms held closely by their side the flailing never starts. Baby will remain calm (unless, of course, there's something else wrong...).
I picked up the technique rather quickly from the nurses at the hospital after William was born.
- Find a soft, flat surface like a bed or couch.
- Lay the swaddling blanket (apparently this is a standard sized thing) in the shape of a diamond on the flat surface.
- Fold the top of the diamond down a little ways (the exact amount is not important).
- Lay the baby on the blanket so the top (folded) edge is behind the baby's neck, above the shoulders.
- Pull the baby's arms down to his/her side and hold them there. The baby will resist, but you can easily overpower a newborn. I find it easiest to hold both arms down with one hand so the other hand is free to fold the blanket, but your hand-size-to-baby-size ratio may be smaller than mine. In that case just hold one arm down at a time and use the blanket to hold the first arm down while you move the second arm into place.
- Fold the left corner of the blanket tightly across the baby's chest, over both arms, and tuck it in just a little bit on the right side of the baby (your right side, baby's left side).
- While still holding the baby's arms down (they could still get loose at this point), fold the bottom corner of the blanket up over the baby's legs and torso.
- While still holding the baby's arms down (they could still get loose at this point), lift the right corner up in the air at about a 45˚ angle and cinch it nice and tight. The tighter you cinch it, the less likely the baby will wiggle his/her way out of the burrito. Just don't hurt the baby.
- Finish folding the right corner around the left side of the baby (your left side, baby's right side).
- Lift the baby slightly and continue to fold the remaining slack under the baby.
At this point the baby should calm down rather quickly.