The first person to start stacking chairs after the event changes what everyone else does next.

Groups wait for a signal about what is expected and then almost everybody copies it. Standing around after something ends is less laziness than uncertainty about whether the work is over. One person picking up a chair settles that question for twenty people without a word being said.

Be first at the unglamorous part this week rather than waiting to be asked. Pick up one thing and keep going quietly. You will not have to recruit anybody, which is the strange part of going first.