First of all, you need to have as many activities going on as you can.
You can set up fitness tests for the individuals deciding to participate, those who see it as some kind of race will really work hard and put determination into it.
You're always going to need people willing to follow all this, so I would personally for my joy, stride in making it worth it, but ALSO more importantly fun.
The goal I would be trying so hard to pursue is to get everyone looking forward to a healthy, and active lifestyle.