Swing. Either in your arms or the mechanical version.
Suck. A finger, knuckle or pacifier will do. Of course, your baby has been fed already.
Shushing. Long stretches of the shushing sound simulate the flow of blood your baby heard in the womb. It works wonders for both baby and caregiver.
Side. Holding baby on their side is comforting to them. The left side is best for digestion, so start with that.
Swaddle. Babies like to feel contained and safe.