The urge to conform to a group norm is powerful. When implementing change, this force can work against you, since no one wants to step out and break the unspoken rules. But, it can also be used to get people to work by a new set of norms as well. To influence change, harness peer pressure.
One way to harness peer pressure is to be very deliberate and open about it. Within a group, explicitly agree on the new way of acting, and commit to a group response when someone strays from the new way. Encourage members of the group to hold each other accountable.
As a facilitator, you can use it more subtly. For example, if you have a couple of members of a team that are not completing their tasks on time, start the meeting with updates from those who have completed theirs first. It will be more evident to the slackers that everyone else is performing their part.
Similarly, you can introduce a new person to an existing group that has already adopted a new behavior. The group will indoctrinate the new person naturally. Once they are done, you can rotate in someone else until everyone is on board with the program.
How might you harness peer pressure?
Read more of the 99 Ways to Influence Change.