In summary: Get involvement and complete backing from the senior management (at least 2 levels up!), make sure goals and objectives are understood, make sure you establish processes which are actually understood and followed by people, check out inertia effects and so on.
In a small group, things work fine because everyone is involved, and it is group effort, and things are likey to succeed. But the moment it is an effort where the audience is not personally in touch with you (i.e. you are doing it for much wider group), then you need to handle it in much more different way (heeding to suggestions such as ones from above link). People come from variety of background; they won't have visibility towards objectives and goals the way you do. Or perhaps, they have some suggestions to give from their experience... In essence, the success factors are not in your hands alone, and you have to take help from senior mentors, and so on.