Starts with simple conversations around interests. An example was some staff getting "Fit Bits" and then conversations were focused on that. Other staff joined to be part of the talk.
Friendly competitions and/or posting health and wellness goals. Not everyone want to compete with others but "putting it out there" keeps you honest and involved.
Make it easy . . . make it site based, which means that if you let staff get away from the work place, they may not continue to participate. Having keen staff members hosting activities allows for others to join. An in-house yoga group after work in a classroom, CrossFit using PE equipment, etc.
Passionate co workers motivate you to want to get up and do something.