People want to have influence and like to feel as if they share power within the organization. Show that you value every person in your organization equally. It'll translate into a more motivated membership. If possible, employ praise and criticism separately. It usually doesn't work as it ends up lessening the impact of both the criticism and the praise, and leaves everyone feeling dissatisfied.
People like to know what exactly they've been called there for.
Don't give mixed signals. Learning to differentiate between the two effectively, can maximize your potential as a motivator. There's no substitute for genuine enthusiasm. Motivators all over the world will tell you that real enthusiasm generates real energy, which can become an irresistible force if you focus it properly. Interact with your members in a positive, energetic manner.