Lead by example--I agree with those who said this and feel this way.
Our club is growing in membership and my feeling is that it is due to the example of fun and sportsmanship we are promoting. We do have some people that either play on, walk the trails or bike our course that leave some trash around but it never ceases to amaze me the amount of other folks that will pick this trash up and carry it to the next receptacle (of which there is one on almost every other hole) myself included. I do not understand throwing trash in the woods like no one will see it...
I even played in a tournament in Memphis a couple weeks ago with a guy(Shannon) from Chattanooga, TN and he picked up all the trash he saw and it wasn't even his course.
There's more good out there than bad, just sadly, the bad gets more noticed.
Lead by example...others will follow.