Teammates need to get to know each other, so they can have candid relationships. So we're back down to the foundation of Pat Lencioni's Pyramid from Five Dysfunctions of Teams. When they do, they care more about each other's approval, ask for help quicker, and hold each other accountable … and so up the pyramid to getting results.
I'd send everyone to a rope's course if we had time. (Or if they wanted to, or if there was a decent ropes course within 2 hours of Manhattan, or if it worked over video conferencing for all of our offices.)