Get/set/start/keep the ball rolling
Definition 1 of 3
Pro Tip 1/3Initiating Action
Use it to express starting a process, often which involves others. 
During the meeting, he said, 'Let's get the ball rolling with introductions.'
Pro Tip 2/3Positive Momentum
It suggests positive progress or momentum in a group task or conversation. 
To energize the team, I said, 'Let's get the ball rolling on brainstorming ideas!'
Pro Tip 3/3Informal Encouragement
It's a less formal way to encourage action, suitable for casual or business discussions. 
Can we get the ball rolling on the project proposal soon?